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Easy Electrical Experiments 

And How to Make Them 



AN ELEMENTARY HAND - BOOK OF LESSONS, 
EXPERIMENTS AND INVENTIONS FOR BEGIN- 
NERS AS WELL AS ADVANCED STUDENTS, 
WRITTEN IN A SIMPLE AND EASILY 
UNDERSTOOD LANGUAGE 



BY 

P. DICKINSON 

w 



FULL Y ILL USTRA TED 




CHICAGO 

FREDERICK J. DRAKE & CO a 

PUBLISHERS 






Copyright, 1903 

By Frederick J. Drake & Co. 

Chicago, 111., U. S. A. 



Copyright, 1918 

By Frederick J. Drake & Co. 

Chicago, 111., U. S. A. 



20 i9!8 



'CI. A 5 0.8-4 8 7 



PREFACE 



The series of electrical experiments which follow were 
originally published in serial form in Popular Mechanics. 
Their appearance in book form is warranted by the very flat- 
tering reception which has been accorded them and the numer- 
ous requests to have the articles in a more permanent shape. 
They have been presented in very nearly the same order as. 
that in which they originally appeared. 

The experiments are designed for those boys who are not so 
fortunate as to possess a large assortment of tools, and who 
have had little training in the use of tools. Were the experi- 
ments designed for trained machinists, with a liberal supply 
of tools and appliances at hand, the designs might in some 
cases be worked out in a more complete and serviceable manner. 
But for the average boy, with few tools, and a desire to learn 
the principles underlying the construction of the more common 
electrical appliances, it is thought that the designs presented 
are far better than more elaborate ones which might be beyond 
his reach. 

The author can only express the wish that the experiments 
in their present form may be of interest to his many young 
friends, whose kind words of approval have been a constant 
source of encouragement 

L. P. Dc 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER I. 



SIMPLE EXPERIMENTAL BATTERY. 



Electricity exists in two forms — as a stationary charge, and as 
a moving current. The former is not of much practical value 
to us, while the latter is of immense value. It is the electric 
current that runs our street cars and lights our houses, and en- 
ables us to do the many other wonderful things with which every 
one is more or less familiar. There are at least three methods 
by which this electric current may be produced, two of which 
are in every day use. One of these methods is to use a Voltaic 
cell, or battery, and the other method is to generate the current 

by means of a dynamo driven 
by a steam engine or other 
source of power. When we 
wish to use current on a 
large scale, the dynamo meth- 
od is much the cheapest to 
use. Butj for all purposes 
where only a small amount of 
current is needed, it is much 
cheaper to generate it by 
means of a battery. 

A powerful and efficient 
battery for experimental pur- 

FIG 1 U A U 

poses can be made by any 
amateur at an insignificant cost. For this purpose there will 
be needed four tumblers (the kind with vertical sides) about 
2 l / 2 inches in internal diameter; four pieces of pine y 2 inch 




2 EASY ELECTRICAL EXPERIMENTS. 

thick and three inches square ; four zinc rods $£ inches in diam- 
eter, such as may be bought at any electrical supply store at 
a cost of a few cents each, and 16 carbon rods, y 2 inch in 
diameter and 5 inches long, such as may be picked up under 
any electric street light. 

Cut a piece of board three inches square and Yi inch thick. 
In the center bore a 3^-inch hole; *A from the center of this 
hole bore four other holes ^ in diameter and equally spaced 
around the central hole. (See Fig. 1.) File every trace of cop- 
per from the surface of the carbon rods (if they are copper 
plated) and having filed them to a length of 5 inches, push four 
of them through the Y 2 holes so that they project 3^ inches 
from the lower side of the board. They should fit snugly, and 
be wedged in if necessary. 

In a tin dish large enough to admit the board which forms 
the top of the cell just made, melt some paraffine wax until it 
just begins to smoke, taking care not to heat it hot enough so 
that it will take fire. Immerse the board and the short pro- 
jecting ends of the carbons in this hot wax, leaving it there for 
five minutes. Do not immerse the long projecting ends of the 
carbon in the* wax, nor get the wax on these ends, for this will 
impair the efficiency of the cell. The object of the wax is to 
make the board and the upper ends of the carbon rods imper- 
vious to acids and moisture. 

Remove the board and carbons from the wax, shake off the 
superfluous wax and let them drain bottom side up, until cool. 
We have now four carbon rods, mounted upon a paraffined 
board, the whole forming one pole of our cell. A zinc rod forms 
the other pole, and one of them should now be pushed through 
the hole in the middle of the board, until it projects the same 
distance from the lower side of the board as the carbon rods 
do. The zinc must not touch the carbon rods, as this would 
spoil the action of the cell. 

All that is left to do now is to connect the carbon rods with 
each other. An easy way to do this is to take a piece of bare 



EASY ELECTRICAL EXPERIMENTS. 




copper wire (not insulated), about six feet long, and wrap it 
tightly around one carbon about ten times, 
then carry it on to the next, wrapping it 
around the second, then on to the rest of the 
carbons. All wax should be scraped off be- 
fore this is done until a clean carbon surface 
is obtained. After wrapping the wire around 
the fourth carbon, twist it about itself two or 
three times, and carry the loose end to a bind- 
ing post screwed to one corner of the board. 
Insert the apparatus just constructed into one 
of the tumblers, and one of the cells is com- 
plete, with the exception, of course, of the 
liquid which is to be used. Its appearance is 
shown in Fig. 2. Proceed in this manner 
with each of the other cells Four is a suffi- 
cient number of cells for most purposes, although the amateur 
may wish to make more for special purpose. 

A liquid for use in these cells can be made as follows : Dis- 
solve 8 oz. of bichromate of potash in two quarts of hot water. 
When cold add 8 oz. commercial sulphuric acid. A caution must 
be given regarding the use of this acid. First, never let it touch 
the fingers or clothing or any similar article. It will destroy 
them like fire. Next, never pour water or any solution into the 
acid. Always pour the acid very slowly into the water, stirring 
constantly. On account of the destructive qualities of this acid, 
it is almost imperative that the tumblers containing it should 
stand on some sort of a tray. This may be made of a shallow 
wooden box about one inch deep, thoroughly soaked in paraffine. 
Whenever the battery is not in use, the carbons and zinc rods 
must be removed from the acid and set aside to drain. The 
tray should be large enough for this purpose.' In using the cells, 
connect the carbon terminal of the first cell to the zinc of the 
second, the carbon of the second to the zinc of the third and 
the carbon of the third to the zinc of the fourth. This will leave 



4 EASY ELECTRICAL EXPERIMENTS. 

free the zinc pole of the first cell and the carbon pole of the 
fourth cell, which will form the terminals of our battery. 

In a later paper, we shall see how we may, by a little extra 
work, improve the working of these cells, and how we may per- 
form many interesting experiments with them. 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER II. 



SIMPLE GALVANOMETER. 



In setting up the battery described in the preceding chapter, 
fill the tumbler about two-thirds full of the solution, place the 
zinc and carbon rods in the solution, and join the cells in the 
manner described — that is, join the zinc pole of the first cell to 
the carbon pole of the next, and so on. Cells joined in this way- 
are said to be in series. In order to show the effects of the 
electric current, two or three simple experiments will be de- 
scribed. 

In an ordinary tumbler prepare a very weak solution of salt 
in water. Run a piece of bare copper wire from the zinc pole of 
the first cell to the tumbler of water, fastening it so that it will 
dip into the water a little way. Run another wire from the car- 
bon pole of the fourth cell, and dipping into the tumbler of water 
but not touching the first wire. If the battery has been set up 
as directed, there will be seen in the water bubbles of gas, which 
rise from around the wires. This may be most plainly seen by 
placing the tumbler between the eye and the light. Break the 
circuit by disconnecting the end of the wire connected to the zinc 
pole of the battery. It will be noticed that the bubbles cease 
instantly. Upon touching the wire again to the zinc, the bubbles 
again appear. Clearly then, there is some process going on in 
the tumbler of water, which is caused by the passage of some 
invisible agent from the battery through the wires to the tumbler. 
That which is flowing in the wire is the electric current. The 
bubbles of gas seen rising through the water are hydrogen and 
oxygen, of which the water is composed. 

The electric current passing through the water decomposes 
it — that is, separates the hydrogen and oxygen. We shall learn 
at some future time how the effect just described is turned to 
good use in the storage battery. 



6 EASY ELECTRICAL EXPERIMENTS. 

Another experiment showing the magnetic effect of the current 
is very interesting. Procure a small pocket compass such as 
may be bought for about twenty-five cents, consisting of a mag- 
netic needle about one inch long, swinging freely on a pivot at 
the center of a circular scale. Such a needle if left to itself will 
point nearly north and south. Having placed it upon a piece of 
board resting on a table, drive two wooden pins into the board 
about six inches apart. 

Adjust the board and the compass so that a wire stretched be- 
tween the two pins will be parallel to the needle, and about one- 
half inch above it. Connect the north end of the wire just men- 
tioned to the carbon pole of the battery, and the south end to the 
zinc pole. 

Note carefully the position of the compass needle before and 
after making the final connection. It will be found that when 
the wire is connected so that a current flows through it, the 
needle is deflected so that its north end points to the east of 
north. Try the same experiment when the wire connecting the 
pins is lowered so as run beneath the needle. Also try the 
effect of reversing the connection of the wires running to the 
battery. Finally wrap a piece of fine insulated wire several times 
around the outside of the compass case, turn the latter until the 
needle is parallel to the wires, and try the effect of connecting 
the terminals of this coil to the battery. 

In all these cases there is an effect produced upon the needle 
by the current, this effect increasing with the number of turns of 
the insulated wire around the compass case. The experiments 
just described will help the student to understand the action 
of the following simple instrument, for the detection of weak 
currents. 

Procure a block of whitewood, two and one-half inches square, 
and one-half inch in thickness. In its center bore a hole just big 
enough to receive the case containing the compass already men- 
tioned, and deep enough to allow the compass to sink in until its 
top is even with the upper surface of the block. On one edge of 
the block cut two slots, each one-half inch in width and three- 



EASY ELECTRICAL EXPERIMENTS. 7 

eighths inch deep. The centers of these slots should be five- 
eighths of an inch from the corners of the block. Do the same, 
with the edge of the block directly opposite to this one. In these 
slots wind ten layers of No. 24 double cotton covered magnet 
wire, as shown in Fig. 1. These are the coils which are to carry 




the current and which are to act upon the needle, causing it to 
deflect when a current passes through them. Beginning with 
the left hand coil, wind it over and around the block until the 
required ten layers is obtained, then cross the wire on the under 
side of the block over to the right hand slot, and without break- 



8 EASY ELECTRICAL EXPERIMENTS. 

ing it, continue winding in the second slot in the same direction 
as the first coil was wound. Some difficulty may be found in 
keeping the layers evenly wound, especially at the middle of 
the coil. It may be necessary to bind the turns of each layer 
together by wrapping a thread around them at this point, before 
winding the next layer. The even winding of each layer is es* 
sential to the good appearance of the completed instrument. 

When the second coil has its ten layers neatly wound, fasten 
the beginning of the first coil and the end of the second to two 
small binding posts. To enable the instrument to stand firmly 
upon a table, glue four cleats one-half inch thick to the under 
side of the board, one at each corner. Give the whole board and 
the coils two coats of brown shellac, and our instrument is com- 
plete. Such an instrument is called a galvanometer, and is a 
very useful piece of apparatus. There are many other forms of 
galvanometer, but their consideration must be left for another 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER III. 



VARIOUS TYPES OF CELLS. 



If the student has experimented with the form of battery de~ 
scribed in Chapter L, he has probably noticed a violent action go- 
ing on in the neighborhood of the zinc rods. Bubbles of gas are 
constantly coming from the solution, whose odor is extremely 
irritating. This gas is hydrogen, and it is set free from the 
acid of which it forms a part, when the latter dissolves the zinc. 
If the zinc rod were perfectly pure, there would be no such ac- 
tion as has been described, if the solution used were of proper 
strength. We could remedy the trouble by using zinc rods which 
are pure, but they are very expensive, and we can secure the 
same result in another way. 

Remove the zinc rods from the solution after they have been 
immersed for three or four minutes, rinse them in clear water, 
and touch the end of one of them to a drop of mercury. Some 
of the latter will adhere to the zinc. Take a piece of cloth, 
and rub the mercury over the lower half of the rod. It will 
spread easily and rapidly, if the zinc be perfectly clean, until 
the lower part of the rod is covered with a bright, shiny layer of 
mercury. This process is called amalgamating the zinc. If 
there are black spots where the mercury does not flow easily, im- 
merse again in the acid, and repeat the process. 

After all the zincs have been thus amalgamated, replace them 
in the cells. There should be hardly any escape of gas now. 

When no current is being taken from a battery, we say that 
is on open circuit. In this condition with zinc rods well amal- 
gamated, there should be hardly any action between the acid 
and the zinc. It is usually the case, however, that the zinc will 
slowly dissolve, even with the precaution just described. So 
the zinc and carbon rods should be removed from the solution. 
when the battery is not in use. 



10 



EASY ELECTRICAL EXPERIMENTS. 



*t 



The neatest way of accomplishing this result is to us 
rangement shown in Fig. i. The tumblers containir 
tion are held in a trough made of pine boards thoroi 
in hot paraffine. At the ends of this trough are t 
pieces about one foot high, which support a horizontal shaft pro- 
vided with a crank, by means of which the rods may be raised 



ar- 

d- 

boiled 
upright 




Fig. i. 

from the solution. Fasten a light strip of pine along each side 
of the square pieces of board which hold the rods, so that the 
latter are rigidly fastened together at the proper distance apart 
to easily fit into the tumblers when they are in the trough. 

Attach the frame work carrying the rods to the horizontal 
shaft above mentioned by cords, so that when the crank is turned 
the rods will be raised from the solution. A ratchet on the 
crank shaft, with a retaining pawl on the upright will enable us 
to leave the rods at any desired height. 



EASY ELECTRICAL EXPERIMENTS. 



II 



T' ^udent must not think that the form of battery which 
ha ^scribed is the only kind that could be made. As a 

matter ct almost any two metals placed in a liquid capable' 

of dissox ^ *g one of the metals more than the other, would give 
us an electric current. To prove this statement and to investi- 
gate the relative values of the different metals for use in gal- 
vanic batteries, the following experiments are interesting: 

Procure small strip or rods of copper, zinc, iron, carbon, 
lead and tin. Prepare also solutions of salt, sulphuric acid (see 
directions in Chapter I), and sal-ammoniac. 

Take any two of the above metals, and immerse them in the 
salt solution. Run wires from the strips to the galvanometer 
just constructed, and notice if the needle moves when you make 
the final connection. Repeat this with the same strips when 
immersed in the other solutions. Try also as many different 
combinations of metals as you have at your disposal. It will be 
noticed that the effect produced upon the needle is stronger in 
some cases than in others. The combination of zinc, carbon, and 



Name of 


Materials 


Solutions 




Cell. 


Used. 


Used. 


E. M. F. 




Zinc 


Zinc Sul. 




Daniell 


Copper 


Copper Sul. 


1.08 




Zinc 


Zinc Sul. 




Gravity 


Copper 
Zinc 


Copper Sul. 


1.08 


Leclanehe 


Carbon 


Sal-Ammoniac 


1.40 




Zinc 


Sul. Acid 




Grove 


Platinum 


Nitric Acid 


i.8a 




Zinc 


Sul. Acid 




Bunsen 


Carbon 


Nitric Acid 


1.80 




Zinc 


Cnromlc Acid 




Poggeudorf 


Carbon 




2.00 




Zinc 


Salt 




Fuller 


Carbon 


Pot. Bi-Chromate 


2.00 




Zinc 


Caustic potash 


0.80 


Edison-^alande 


Copper 







sulphuric acid will probably be found to produce the most marked 
effect. But for some purposes other combinations are used. For 
instance, if we wished to make a battery to ring an electric bell, 
we would use zinc and carbon rods, and a solution of sal- 
ammoniac. 



12 EASY ELECTRICAL EXPERIMENTS. 

Each different combination has received a special name, gen- 
erally that of the man who invented it. A few of these are 
given in the following table. It will be noticed that many of 
the cells use two liquids. This is for the purpose of keeping the 
current constant, as it is found that the strength of the current 
falls off after a little, when only a single liquid is used The 
abbreviation E. M. F. stands for electro motive force. 



EASY ELECTRICAL EXPERIMENTS. 15 

CHAPTER IV. 



HOW TO MAKE A TANGENT GALVANOMETER. 



In chapter two, directions were given for making a galvan- 
ometer for the detection of electric currents. Wlhile an instru- 
ment such as was there described is very useful for general test- 
ing purposes, it is not at ail suitable for the measurement of cur- 
rents. The tangent galvanometer, on the other hand, is an in- 
strument in which the parts are so related that we can readily 
calculate the strength of the current flowing through it. 

To make such an instrument, take a piece of whitewood }4 
inch thick, and saw out of it a ring whose outer diameter, is 
10Y2) inches, and whose inner diameter is 9 inches. 

Cut two similar rings from a piece of whitewood % inch 
thick, the rings in this case being 11 inches in outer diameter r 
and 9 inches in inner diameter. Glue these pieces together so 
that the thicker ring is between the two thinner ones, forming a. 
ring with a channel on its outer surface which is J4 hich. deep 
and y 2 inch wide. 

From another piece of whitewood % inch thick cut a cir- 
cular piece 11 inches in diameter. In trie center of this cut a- 
hole 6 5-16 inches in length, and 1 inch wide. This last piece 
is to serve as a base upon which the ring is to be supported ver- 
tically. Three cleats Yz inch square should be glued to the bot- 
tom of the board to serve as supports for the instrument. 

The arrangement is clearly shown in the accompanying figure. 

The ring should fit into the slot in the base so that its inner 
surface is just even with the upper surface of the base board, and 
is secured by a small strip screwed to the base board as shown. 

The cutting of these circular pieces is not at all difficult if 
a band saw driven by power be used, such as almost every fair 
sized carpenter shop should possess. It can be done, however, 
by means of an ordinary key-hole saw. 



14 



EASY ELECTRICAL EXPERIMENTS. 



Before mounting the ring upon its base, wind in the groove 
upon its circumference eight turns of No. 16 double cotton cov- 
ered magnet wire. Fasten the loose ends together with a string 
temporarily. Across the two flat sides of the ring fasten two 
.strips of whitewood Y% inches wide, yi inch thick, and n inches 




TANGENT GALVANOMETER 



long. These should be fastened so that their upper edges pass 
exactly through the center of the ring. 

Procure an ordinary pocket compass about ij4 inches in diam- 
eter and cut grooves in the middle of the last mentioned strips, 



EASY ELECTRICAL EXPERIMENTS. i$ 

with the center of the needle exactly at tne center of the coil. 
Its zero mark should lie half way Between ttie two strips. 

Now place the ring supporting the compass at its center, into 
the slot in the base board, connect the two ends of the wire to 
two binding posts, give the whole a coat of brown shellac, and 
the instrument is ready for service. All dimensions given are 
very important. Any deviation from them will introduce errors 
in the results obtained by its use. 

To use the instrument, first remove from its neighborhood all 
pieces of iron or steel, especially any magnets that may be in 
the vicinity. At this point it may be mentioned that all screws 
used in the instrument should be made of brass. Set the gal- 
vanometer upon a level table, and turn it until the needle, 
pointing north and south, and swinging freely, lies exactly in the 
plane of the coil. If the directions regarding the mounting of 
the needle have been followed, it will then point to zero. Send 
the current from one cell of battery through the coils. The 
needle will be deflected to the one side or the other, and will 
finally come to rest at a certain angle, — let us say 45 degrees. 
The dimensions of the instrument have been so chosen that 
when the deflection is 45 degrees, the current flowing through the 
coils upon the ring is one-half an ampere. The ampere is the 
unit chosen to designate the strength of an electric current 
For other angles, the value of the current may be found from the 
following table: 

Angles. Current. *. 

10 degrees 088 amp. 

20 " 182 "* 

30 " 289 " 

40 " 420 " 

45 " 50O " 

50 " 600 " 

55 " 7i5 - 

60 , " 865 " 

70 " 1.375 - 



16 EASY ELECTRICAL EXPERIMENTS. 

Since the force with which the earth acts upon a magnetic 
needle \aries for different places, the values just given for the 
current will not be true for all parts of the country. The table 
gives correct values for the immediate vicinity of Chicago, and 
for that section of the United States lying east of Chicago, and 
north of the Ohio River. For places south of the Ohio and 
east of the Mississippi, the results given in the table for the 
values of current should be multiplied by 1.3. 



EASY ELECTRICAL EXPERIMENTS. 17 



CHAPTER V. 



MAGNETISM. 



Nearly every one is familiar with the effects produced by the 
small steel "horse-shoe" magnets, so common in the amateur 
experimenter's laboratory. They have the property of attracting 
to themselves pieces of iron and steel when small bits of these 
metals are placed near them. Indeed, a magnet has the power of 
communicating its magnetism permanently to other bodies, such 
as needles and tools made of steel. Many a boy has magnetized 
his knife by rubbing it over a magnet, so that it will pick up 
needles and pins and other small articles. The strangest part of 
it is that from one magnet we can make a thousand other mag- 
nets by rubbing bits of steel over it, without in the least weaken- 
ing the original magnet. What is this force which we call mag- 
netism? Clearly it is not a fluid, as was formerly supposed; for 
a magnetized bar weighs no more than an unmagnetized one. 
And how could a magnet communicate some of its magnetism to 
another body, without losing some of its own properties, if the 
magnetic effects were dependent upon some fluid residing within 
the metal? Clearly the only difference between a magnetized and 
an unmagnetized body must be a difference in their internal con- 
ditions. 

Every magnet has two poles, usually at its ends. Around these 
poles there is a region where the magnetism is especially notice- 
able. Pieces of steel placed there will be attracted or repelled. A 
straight bar of magnetized steel, if hung up by a thread at its 
center so as to hang horizontally, will turn so as to point north 
and south. The same end always points to the north, and is 
called the north pole of the magnet, the opposite end being called 
the south pole. If two magnets be brought close together, so that 
their north poles are near each other, they will repel. But if the 



18 EASY ELECTRICAL EXPERIMENTS. 

south pole of one be presented to the north pole of the other, 
they will attract. The student may easily verify these statements 
by using magnetized sewing needles, suspended by fine silk 
threads. 

A very pretty experiment is as follows : — 

Procure a small horseshoe magnet, about six inches long. 
Place it horizontally upon a sunny window sill, and having low- 
ered the window shade, cover the magnet with a piece of blue 
print paper such as amateur photographers commonly use. 
Sprinkle upon this some very fine iron filings, holding the hand 
some distance above the magnet, and sifting the filings slowly 
through the fingers. Tap the paper gently to make the filings 
arrange themselves in regular lines. Now raise the shade, and 
allow the sun to shine upon the blueprint paper for about five 
minutes. Then shake off the filings, and place the paper in a 
dish of water. A beautiful picture of the magnetic field around 
the magnet will be obtained. The experiment may be varied by 
using a photographic plate, exposing it to lamplight instead of 
daylight, thus obtaining a negative from which a fine print may 
be made. 

Electric currents may be made to produce magnets. Many per- 
sons for this reason confuse magnetism and electricity, supposing 
them to be one and the same thing, but they are not. A power- 
ful magnet operated by an electric current may be made as fol- 
lows : 

Have a blacksmith cut for you a rod of soft iron or steel, 12 
inches long and Y% inch in diameter. After being cut it should 
be bent into the form of the letter U, with the parallel arms of 
the bar about 1% inches apart. Make two wooden spools, each 
2V2 inches long and 1^4 inches in external diameter. There 
should be a hole through the center of each spool, Y% inch in 
diameter, so that they will slip on the arms of the iron bar just 
described. These spools are, of course, best made in a lathe, 
but the writer has made them with no tools but a ^ inch bit, and 
brace, and a sharp jack knife. In the latter case it is better to 



EASY ELECTRICAL EXPERIMENTS. 



19 



cut out the shank of the spool separate from the ends of the 
spool, and to glue the parts together with the aid of a few small 
brads. The shank of the spool should be as thin as is consistent 
with mechanical strength. 




On each spool wind nine layers of No. 18 double cotton cov- 
ered magnet wire. Be sure and wind each layer evenly and 
tightly, as this adds much to the appearance of the finished coil. 
When wound, slip the two spools of wire upon the iron core, and 
wedge them tightly in place. Connect one end of the first coil 



20 EASY ELECTRICAL EXPERIMENTS. 

to one end of the second coil. Be sure, however, that they are 
connected in the following manner. Holding the magnet with 
its ends toward you, imagine a current to be flowing into one 
terminal of the left hand coil and out at the other, so as to go 
around the magnet core in the same direction as the hands of 
a clock move. Connect the terminal of the first coil by which 
the current leaves the coil to one terminal of the second coil, in 
such a manner that the current will go around the seond coil 
in a direction opposite to that in which the hands of a clock 
move. Looking at the end of the magnet, the current will seem 
to trace a figure 8 in going around the coils. Connect the two 
loose terminals to a powerful battery, and it will be found that 
the iron core becomes strongly magnetized whenever a current 
flows through the coils, but that it loses nearly all its magnetism 
as soon as the current ceases. 



EASY ELECTRICAL EXPERIMENTS. 



21 



CHAPTER VI. 



HOW TO MAKE AN INDUCTION COIL. 



A most interesting piece of apparatus and one that is quits 
easily made, is an induction coil. The present chapter deals with 
the construction of such a coil which may be used for medical 
purposes, or for general experiments. 

An induction coil consists of four esential parts. These are, 
(i) a core of soft iron; (2) a primary coil of a few turns, wound 
close to the core; (3) a secondary coil of many turns wound 
outside the primary coil, but separated from it, and (4) a device 
for rapidly making and breaking the current which flows through 
the primary coil. An inspection of the accompanying figure 




will show the relation of these four parts. The core "C" is 
made up of a bundle of soft iron wires, very straight, and ac- 
curately cut to a length of 4^4 inches. The wires should be 
bound together very tightly, forming a core, when completed, 
whose diameter is J4 inch, measured just outside the iron. The 
wrapping should be done with stout linen thread, wound very 
tightly and close together, leaving, however, a bare space at one 
end of core for a distance of 24 mcn from the end. 

For the shank of the spool which is to support the coil, make 
a wooden cylinder % inch outside diameter, and 4K inch 



22 EASY ELECTRICAL EXPERIMENTS. 

long, with a Yz inch hole through its entire length. This leaves 
a thickness of only 1-16 inch for the material forming the spool, 
and is in consequence a little difficult to make. The best way 
is to bore a Y2 inch hole lengthwise through a block of wood 
of considerable size, and then turn or whittle the block down 
until it is of the required outside diameter. For the heads of the 
spool take two pieces of whitewood, Y2 inch thick and 2 inches 
square, and bore in the center of each a Y% inch hole. The shank 
just constructed should fit tightly in these holes and be glued 
in place, forming a spool with square heads and a round shank, 
with a Yz inch hole running throughout its entire length. 

The iron core first made is supported from one end only, 
in the figure the right hand end. Make a plug, slightly 
tapering, which will just fit the Y2 inch hole in the end of the 
spool. Bore through its center a hole which will fit tightly 
around the iron core. Drive the core into the plug, and drive 
the latter into the hole in the end of the spool, making a tight 
fit in each case. The core will then be supported by the plug, 
and should project Ya i R ch from the end of the spool. 

We are now all ready for making a device for varying the 
strength of the "shock" obtained from the coil. This consists 
of a tube, shown at "T," which is made of metal and slips over 
the iron core, and into the inside of the hole in the wooden spool. 
This is why we supported the iron core from only one end, 
so that we could leave the other end free for the insertion of this 
tube. Procure some very thin sheet copper or brass, or even 
tin, and bend some of it into the form of a tube 4j4 inches 
long and 7-16 inch in external diameter, and solder it smoothly. 
It should slip easily into the space between the iron core and 
the spool. The soldering is very important for the proper work- 
ing of the coil. Perhaps some of those who read this may be 
so fortunate as to secure a thin piece of brass tubing at a hard- 
ware store, of the proper dimensions. If so, this is much the 
best plan. Fit to one end of the tube a wooden handle, and 



EASY ELECTRICAL EXPERIMENTS. 23 

adjust the tube until it slides in and out freely in the space 
provided. 

Upon the spool wind three layers of No. 18 double cotton cov- 
ered magnet wire. The ends should project through small holes 
in the head of the spool. This forms the primary coil. Wind 
two layers of -stiff writing paper outside this, gluing it in place, 
and paying special attention to the ends of the spool where the 
paper should fit tightly against the heads. Outside this wind 
5 oz. of No. 36 double silk covered magnet wire. This ought 
to make a secondary coil of a depth of about Y% inch. Con- 
nect its terminals to two binding posts "B," as shown. Be very 
careful in handling this wire, as it breaks very easily. Do not 
try to wind it from a loose coil, as it is sure to snarl and break. 
Support it upon a reel or spool from which it may be directly 
wound to the coil. The inside terminal of this secondary coil 
should pass through a small hole in the end of the spool. This 
is necessary to prevent short circuiting the coil. 

The circuit breaker shown at "H" is made of a piece of soft 
iron attached to the very thin spring "S," which is screwed to 
the baseboard. Pressing against this is the screw "P," made of 
brass, and supported as shown. Connect one terminal "Y" of 
the primary coil to this spring. Connect one pole of a strong 
battery to "P" and the other to "W" and the hammer "H" will 
begin to fly back and forth very rapidly, making and breaking 
the circuit between "S" and "P" at every movement. It may 
be necessary to turn "S" so as to secure the proper relation be- 
tween the different parts. The hammer "H" should be about 
% inch from the end of the core. 

On connecting two wires to the binding posts marked "B," a 
current will be obtained capable of giving shocks to the persons 
holding the wires. The strength of these shocks may be varied 
by sliding the tube "T" in and out, the shocks being the weak- 
est when it is pushed in as far as it will go. 



24 EASY ELECTRICAL EXPERIMENTS. 



CHAPTER VII 



A SIMPLE ELECTRIC MOTOR. 



An electric motor has three esential parts. These are (i) 
a magnet capable of furnishing a powerful magnetic field; (2) 
an armature, turning in this field, carrying the current which 
drives the motor; and (3) a commutator for leading the cur- 
rent into the revolving armature. In the simple motor about to 
be described, the first of these, the field magnet, is made of two 
6-inch horse-shoe magnets, such as may be bought for about 
twenty-five cents each. The armature consists of two simple 
coils, and the commutator is simply a cylinder of brass, split 
lengthwise into two sections. 

To make the armature, proceed as follows : From a rod of 
soft iron Y inch in diameter cut two pieces iY inches long. 
Wrap each one with a layer of stout paper, gluing it smoothly 
in place. Upon each wind a coil of No. 24 double cotton cov- 
ered magnet wire, each coil being 1Y2 inches long and Y inch 
in external diameter. These coils may best be made by making 
wooden heads, Y inch in diameter, for the end of the coils, with 
a hole in their centers of such size that they will fit tightly upon 
the iron core. Drive them on to the iron core so that they leave 
a clear space at each end of Y inch. Then wind the space be- 
tween them with wire as just explained. Great pains must be 
taken to have both spools evenly wound and of the same size 
and weight. Take a piece of brass rod 3-16 inch in diameter, 
6 inches long, and perfectly straight. This is for the shaft. Cut 
from a piece of brass 1-1(3 inch thick two pieces, each V/2 inches 
long and Yz wide. Bore three holes in each. The first of these 
holes is at the center and is 3-16 inch in diameter. The other 
two holes are Y* m ch each side pf the center and are % inch in 
diameter. 

Having made the coils as directed, mount them upon the shaft, 



EASY ELECTRICAL EXPERIMENTS. 25 

as shown in the figure. The two brass strips are slipped upon 
the shaft, and with the latter passing through the center holes 
and the iron cores slipping into the outer holes in each. Pre.33 
the strips tightly against the coils, and solder the strips firmly 
to the brass shaft, thus fastening the coils firmly to the shaft 
and in the middle of the latter. Connect one terminal of one 
coil to one terminal of the other in such a way that the current 
will go around one coil in a direction opposite to that in which 
it goei around the other. Leave the remaining two ends hang- 
ing free for the present 

The commutator should next be made. To do this mount 
tightly upon the shaft a block of hard wood J4 mcn l° n g an d §4 
inch in diameter. This wooden cylinder revolves with the shaft. 
It should fit the latter tightly and its outer end is Y 2 inch from 
the end of the shaft. Take a thin piece 01 sheet copper and bend 
it into the form of a hollow cylinder Y\ inch long, of such size 
as to just fit upon the wooden cylinder upon the shaft Fasten :.: 
there with eight of the smallest brass screws obtainable. These 
screws should be equally spaced, four on each end, and on no 
account should they be long enough to strike through and touch 
the shaft, as this will spoil the commutator. After this cylinder 
is in place, cut it with a file into two equal sections, with the 
spaces dividing these sections running the same way as the 
shaft. The two sections must be entirely separated so that 
there is no electrical connection between them. 

Wrap the shaft between the commutator and the coils with a 
layer of thin paper, and run each of the two free ends of the 
coils to a section of the commutator. Between the commutator 
and the coils these wires should lie close against the shaft, but 
separated from it by the layer of paper just mentioned, and 
separated from each other. They should be tightly bound to 
the shaft by close wrappings of fine silk thread. The appear- 
ance of the finished armature is shown in the figure. 

The field magnets are two 6-inch horseshoe magnets, such as 
may be easily secured. Be sure and select two which have at 



26 



EASY ELECTRICAL EXPERIMENTS. 




EASY ELECTRICAL EXPERIMENTS. 27 

least % inch clearance between their poles. The shaft just de- 
scribed has to revolve in the space between the poles, and this 
will be a difficult matter to arrange if the magnet poles are 
closer together than % inch. Indeed, it may be necessary to file 
the shaft a little at the points where it passes between the poles, 
in order to allow the shaft to turn freely when the conducting 
wires are in place upon it. 

To support the magnets, fasten a block of wood to a suitable 
base board, the dimensions of the block being 3 inches by 1^ 
inches by 4 inches. The block should be placed with its narrow 
face even with the edge of the board, and with the long axis of 
this face in a vertical position. Fasten the magnets to the sides 
of this block by cleats, held on by screws, thus enabling us to 
vary the position of the magnets until they are exactly right, 
when by tightening the screws they will immediately be clamped 
in place. , 

Support the armature as shown in the picture between the 
poles of the magnets. Two precautions are necessary. First, 
be sure that the north pole of one magnet and the south pole of 
the other are uppermost. This can be determined by trial, al- 
though the north pole of a magnet is usually stamped "N." 
Next, be sure when the coils are so placed that one is directly 
above the other that the commutator is so fixed upon the shaft 
that the two slots are horizontal. 

The supports for the shaft may be made of two blocks of 
wood. A piece of brass screwed to each, with a hole just large 
enough to allow the shaft to turn freely, will make a fairly good 
bearing. 

Fasten two springs of very thin brass to the base board, and 
adjust each until it bears firmly upon the commutator. Upon 
connecting the two brushes to a battery of four or five bi-chro- 
mate cells, the motor will revolve very rapidly and with con- 
siderable power. 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER VIII. 



ELECTRIC UNITS. 



One of the most important points in the study of electricity 
is to get accustomed to the use of electrical units, and to learn 
how to use them intelligently. The chief trouble arises from the 
peculiar nature of the agent with which we are dealing, and the 
peculiar names given to the units. 

It is clear to every one who has experimented at all with elec- 
tricity, that there is something in every electrical circuit which 
forces the current to flow through that circuit. That which 
causes the current to flow has received the name electro-motive 
force (E. M. F.). Now to express the value of any electro- 
motive force, we must have a unit of electro-motive force. This 
unit has received the name volt, in honor of Volta, one of the 
early experimenters in electricity. 

Now the very existence of this electro-motive force proves 
that there must be something about an electric conductor by 
reason of which it tends to oppose the passage of the current. 
If there were no opposition to the passage of the current, there 
would be no need of an E. M. F. to cause the current to flow. 
This property which all bodies possess to a greater or less de- 
gree, of resisting the passage of a current, is called resistance. 
The unit of resistance is called the ohm, in honor of Dr. Ohm, 
a celebrated German scientist. 

An electro-motive force acting upon a given resistance causes 
a current to flow through the latter. Now this current may be 
strong and it may be weak, depending for its value upon two 
things. If the E. M. F. be high and the resistance low, the 
value of the current will be large. But if the resistance be very 
high, the current may be very small even though the *E. M. F. 
be large. So we see that a circuit with a high E. M. F. in it 



EASY ELECTRICAL EXPERIMENTS. 



29 



will not necessarily produce a strong current, unless the resist- 
ance be low. The number of volts in a circuit gives us no idea 
of the strength of the current, until we know the resistance of 
the circuit. The strength of the current is expressed in amperes. 
There is a simple law connecting the values of current, E. M. F. 




***=■ 



Circuit of Water. 
in volts, divided by the resistance in ohms. This is a very im- 
portant law and every student of electricity should become famil- 
iar with it. Thus, suppose that we know the resistance of an 
incandescent lamp to be 200 ohms. What current will flow 
through it when it is attached to a no volt circuit? According 
to the rule just given the current is no divided by 220, or J£ 
ampere. 



30 



EASY ELECTRICAL EXPERIMENTS. 



u 



\^r 



BH 



^ 



O 



Electrical Circuit. 



Very much the same conditions are met with in the circula- 
tion of water in the system illustrated in the accompanying fig- 
ure, "Circuit of Water." 

Suppose the tank A to be partly filled with water, and that a 



EASY ELECTRICAL EXPERIMENT'S. 2>i 

pipe connects it with B and C. Because of the difference in 
level between A and B or B and C water will flow downward 
through the system. There will be friction between the moving 
water and the pipes and the rate of flow of water will depend 
not only upon the difference in level between the tanks, but also 
upon the frictional resistance met with in the piping. At P is a 
pump to raise the water from C back to A as fast as it flows 
down into C. What pressure must this pump exert? Clearly it 
must exert a pressure equal to that between A and B, plus that 
between B and C, plus whatever back pressure results from 
friction. 

Now consider the diagram "Electrical Circuit." It has been 
lettered to correspond with the hydrodynamic diagram just de- 
scribed. Current will flow from A to B through the connecting 
wire if there is a difference of potential (electrical level) be- 
tween the two points. Similarly, there will be a flow of current 
from B to C, if B be at a higher potential (electrical level) than 
C. This flow of current will, however, be opposed by the elec- 
trical resistance of the conducting wires. To make the flow con- 
tinuous, there must be something at P capable of forcing the 
current back to A again. The apparatus to accomplish this is an 
electric battery, which we have already studied. The power 
which it possesses of sending the current through the electrical 
circuit is called electro-motive force, and in the case just illus- 
trated, is equal to the sum of the difference of potential between 
A and B plus that between B and C, plus whatever difference of 
potential is necessary to send the current through the remain- 
ing portions of the circuit including the battery itself. 

Thus we see that difference of level in the case of a water 
circuit is very smilar to the term difference of potential that we 
measure, as the electro-motive force in a circuit often has to be 
obtained by calculation. In the same way, frictional resistance 
to moving water is in some respects similar to electrical resist- 
ance, though the comparison must not be carried too far. And 



32 EASY ELECTRICAL EXPERIMENTS. 

finally, the rate of flow of water through the system described, 
expressed in cu. ft. per second, is very similar in its significance 
to the term "strength of current" in an electrical circuit 



EASY ELECTRICAL EXPERIMENTS. 



33 



CHAP. IX —HOW TO MAKE A 1-20 H. P. MOTOR. 



THE ARMATURE AND COMMUTATOR. 



If the directions given in the last paper for winding the arma- 
ture have been followed, the entire surface of the latter will 
have been covered with four layers of wire, distributed in 
twelve coils, each coil terminating in two wires whose tagged 




ARMATURE-AND COMMUTATOR 






COMMUTATOR 




SIDE: VIEW 



END VIEW 



ends project from one end of the armature. The first thing to 
do after seeing that the winding is smoothly in place is to apply 
what are called "binding wires." These are shown at B in the 
figure, and are for the purpose of holding the wires firmly in 
place when the armature rotates rapidly. The wires tend to fly 
outward, and they must be held tightly to the core by wires 



34 EASY ELECTRICAL EXPERIMENTS. 

wound around the finished armature. Wind a strip of heavy 
wrapping paper Y 2 inch wide completely around the armature 
near one end, and upon this strip wind six complete turns of 
No. 20 brass wire. This wire should be drawn very tight, and 
should be evenly wound. Solder it smoothly at two or three 
different points around the armature, and cut off the ends very 
close and smoothly, so that there will be no sharp points project- 
ing. All superfluous solder should be smoothed off with a file, 
so that the armature may rotate very close to an iron pole piece 
without striking the latter. Wind a similar coil of brass wire 
at the other end of the armature protecting the wires by a heavy 
strip of paper as before. 

Now we come to the making of an important part of our motor, 
called the commutator. Turn out a piece of hard wood of the 
shape shown in the side view of the commutator. The hub, or 
smaller part, is % inch in diameter and Y% inch long. The flange, 
or larger part, is 2 inches in diameter and %. inch thick. 
Through the center is a hole just large enough so that the 
wooden spool will slip tightly upon the shaft. It must fit so 
tightly that it turns upon the shaft with difficulty. 

Now cut out of a piece of sheet copper a circle iJ4 inches in 
diameter. Bore a hole through its center % inch in diameter. 
Then divide the circular copper disc into twelve equal parts by 
lines running through the center. This can easily be done by 
drawing two lines through the center at right angles, which will 
divide the circular disc into four equal parts. Then divide each 
of the four sections into three parts, and this will make twelve 
sections into which the circle is divided. With a sharp-pointed 
knife cut this disc into twelve parts by drawing the point con- 
tinually back and forth over these lines, using considerable 
pressure. It may dull the point of the knife somewhat, but if 
an old knife be used it will do no harm. There will then be 
twelve copper sectors of the shape shown at S. 

Now draw on the outer face of the wooden spool just made a 
circle ij4 inches in diameter. Divide it into twelve equal parts 
by lines running through the center. Place each of the copper 



EASY ELECTRICAL EXPERIMENTS. 35 

sectors just made so that its broad end just coincides with this 
circle, and so that it lies exactly in the center of one of the sec- 
tions just marked upon the wooden disc. Fasten it there by a 
Y% inch round-headed brass screw at its large end, and by a 
very small brad, driven through the copper strip as close as is 
possible, to the inner end of the latter. Fasten the remainder of 
the twelve strips in a similar manner to the wooden disc. As 
the copper sectors were cut from a 1% inch circle, and the circle 
upon the disc is 1^ inches in diameter, there will be a space 
between each copper sector and its neighbor about 1-16 inch 
wide. Be very sure that there is no metallic connection between 
any two of the strips. They must not touch each other nor the 
shaft, nor must the brad which holds one strip touch the brad 
which holds the next strip, nor should it touch the shaft. 

Number these sectors from 1 to 12. Slip the commutator 
upon the shaft, so that sector No. 1 is opposite to coil No. 1, 
with the copper sectors facing outward. Then connect the end 
of coil No. 1 (E-i) and the beginning of coil No.' 2 (B-2) to 
sector No. 1. Connect the end of coil No. 2 (E-2) and the be- 
ginning of coil No. 3 (B-3) to sector No. 2. Proceed in this 
manner, connecting the end of each coil and the beginning of the 
next coil to a sector in the commutator. When you have gone 
clear around the armature, connect the end of coil No. 12 and 
the beginning of coil No. 1 to sector No. 12 of the commutator. 
These connections should be made by twisting the two wires to- 
gether and passing one of them through a hole in the wooden 
spool just above each sector, and clamping it firmly under the 
brass screw. Draw all wires as tight as possible, and be sure 
that the commutator is tight against the armature coils. 



36 EASY ELECTRICAL EXPERIMENTS. 



CHAP. X —HOW TO MAKE A 1-20 H. P. MOTOR, 



THE FIELD MAGNET. 



In the preceding chapters directions have been given for con- 
structing the armature, or the rotating part of the motor. Be- 
sides this, there must be constructed the field magnet, which 
surrounds the armature, and furnishes the magnetic field which 
causes the armature to rotate. 

The field magnet frame must be of iron, and this is where the 
main difficulty comes in. The best form of frame could be made 
by having it cast to the proper shape. But not every boy is sit- 
uated so as to have access to a foundry, and besides, the difficulty 
of constructing patterns properly would make it inadvisable to 
attempt this method of construction. The form described in this 
chapter has been designed with the idea that everybody has 
access to a blacksmith shop, and can readily induce the man at 
the anvil to do the necessary work, which is very simple. 

The form of the field magnets is clearly shown in Fig. I, where 
A represents pieces of iron, bent into the shape shown, and 
bolted together at the top, with a piece of iron, B, clamped be- 
tween them. The strips A are made of a piece of iron bar J4 
inch thick, 1% inches wide and about 8 inches long. As shown 
in Fig. 2 there are four of these strips bolted to a piece of iron 
at the top. 

It may be well to state that the reader may exercise consider- 
able ingenuity in the choice of arrangement of his material. 
That is, if it should happen that no iron stock is available whose 
dimensions are the same as those given, then the amateur can 
modify the dimensions given to conform to his particular case. 
Be very sure, however, that the diameter of the circular chamber 
at the bottom of the magnet is exactly 2.y 2 inches. Too much 
care cannot be exercised in making the iron conform to the right 
shape and dimensions at this point. For this reason it is well to 



EASY ELECTRICAL EXPERIMENTS. 



37 



cut a circular disc from a piece of thin sheet iron, of a diameter 
of 2J/2 inches. By holding this against the curved portion, on the 
inside face of the iron, any irregularity in the shape of the iron 
can be quickly detected. 



c 



T 



'f- 




F"f"T 



e io|od 



...J 



'**,. 




4. 

CO 



r^ 




The iron block shown at B is 1% inches wide, 1 inch thick and 
2Y 2 inches long. Here again the amateur may, if necessary, use 
two blocks of iron instead of one, if a piece of iron of the right 



38 



EASY ELECTRICAL EXPERIMENTS. 



shape be not availably but the dimensions and construction given 
are thought to be the simplest and best. 

Having caused four pieces of iron of the shape and dimensions 
shown at A to be constructed, have a machinist bore a J^-inch 





Frs 2. 

hole through each at the top, the hole being in the center and at 
a distance of J4 inch from the end of the bar. Having procured 
a block of iron such as is shown at B, and of the size, just given, 



EASY ELECTRICAL EXPERIMENTS. 39 

have two 2^-inch holes bored through it from one of the i-inch 
faces to the other. These holes should be so placed that the 
strips when bolted to the iron block will lie closely together, with 
their outer edges even with the ends of the block. Procure two 
bolts (preferably with square heads) Y% inch in diameter and 2^/2 
inches long. These are for the purpose of clamping the pieces 
to the block. Before this is done, however, have a Y^-moh hole 
drilled through the projecting foot at the bottom of each iron 
strip so as to be able to screw the pieces firmly to a board. 

With a file smooth off the faces of the block B, and the inside 
faces of the strips A, so that they will fit smoothly together. 
Then bolt them together tightly. Then test the circular cham- 
ber at the bottom to see if it is of the right diameter and form. 
If there are any irregularities in it smooth them off with a coarse 
file. If the faces of the iron block at the top are not square, it 
may be found that the iron strips are not in line. File the block 
until it is of the right shape to make the strips lie parallel and 
in line. 

Procure a piece of board for a base, 1 inch thick, 12 inches 
long and 6 inches wide. Mount the field magnet frame upon this 
board in its center, by means of heavy screws passing through 
the holes in the projecting feet at the bottom. Be sure that the 
magnet frame is parallel with the edges of the board and in its 
center. 



40 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XI —HOW TO MAKE A 1-20 H. P. MOTOR. 



WINDING (THE FIELD MAGNET. 



Having made the frame of the field magnet, the next thing is 
to wind the coils of wire upon the frame, which are to excite 
the magnet. For this purpose there will be required four pounds 
of No. 16 double cotton covered magnet wire. Make also four 
pieces of wood, Y% inch thick, 354 inches long, and i J / 2 inches 
wide. In the middle of each of these cut a slot % inch wide 
and 2j4 inches long. These are to form the ends of the coils 




Fig 



of wire and are for the purpose of holding the wire in place. 
Smooth them off nicely with sand paper, and round the corners 
a little. Unclamp the magnet frame from the iron block and 
clamp the two pieces forming one side firmly in a vise. In this 
way they are firmly held in position until the wooden strips 
just mentioned are in place, and the wire is wound. 
The manner of fastening the strips in place upon the core is 



EASY ELECTRICAL EXPERIMENTS. 



41 



shown in Fig. I. Make four strips out of fairly thick sheet iron, 
y 2 inch wide and 3 inches long. These are shown at S in Fig. 1. 
With a knife, cut away a little from the inside of the slots in 
the wooden heads of the coil so that they will slip on to the iron 
cores and at the same time allow the strips of sheet iron to be 




inserted between the iron and the wood. Then bend the ends 
of the iron strips up at right angles, so that there will be a free 
space between the wooden strips 2 inches long. There should 
be two of the iron strips on each side of each iron core. Now 
slip the strips and the pieces of wood mounted as in Fig. 1 
along the iron core so that the upper one is 1 inch from the 
upper end of the iron core. To fasten it there, apply a coating 
of glue (not mucilage) to the surface of the iron between the 
wooden strips, and wrap firmly around it two layers of heavy 
paper, two inches wide. This paper is for two purposes. First, 
it holds the iron strips and the wooden heads firmly in place* 



42 EASY ELECTRICAL EXPERIMENTS. 

Second, it protects the iron core so that the wire to be wound 
upon it shall not touch the iron. 

In the space thus formed on each pair of iron cores is to be 
wound 10 layers of the magnet wire already mentioned. In 
starting the winding bore a small hole through the lower of the 
wooden strips close to the core, on the outside of the frame. 
Through this hole pass the beginning of the wire which is to 
form the coil. Then wind ten layers very smoothly and evenly. 
It will be necessary to hold the iron core firmly in this and the 
other operations by clamping one end of it in a vise. After the 
coil is complete, fasten the outer end so that it cannot uncoil, 
and then put the frame together by means of the bolts at the 
top. Connect one terminal of one coil to one terminal of 
the other in such a way that the current going around one coil 
in a certain direction will go around the second coil in the oppo- 
site direction. That is, the current would trace an imaginary 
letter S in going around the two coils. The appearance of the 
finished magnet is shown in Fig. 2. 

The supports for the shaft next claim our attention. Direc- 
tions were given in the preceding paper for mounting the field 
magnet upon the base board. At one end of the board, and at 
a distance of 2% inches from that end of the field magnet, mount 
.a piece of wood, cut from a board % inches thick. This piece 
of wood is tapering in shape, being three inches wide at the bot- 
tom, tapering to two inches in width at the top. Its height is 
2J4 inches. It is to be placed so that its center is on a line 
drawn lengthwise through the center of the board, and is at 
right angles to this line. It is fastened to the board by screws 
passing upward through the base board. The distance of 2^ 
inches mentioned is measured between the end of the magnet 
frame and the inside edge of the upright strip. 

At the other end of the board is another exactly similar piece, 
only it is at a distance of i$i inches from the magnet frame. 
These uprights are shown at B and C in Fig. 2. 



EASY ELECTRICAL EXPERIMENTS. 



43 



CHAP. XII —HOW TO MAKE A 1-20 H. P. MOTOR. 



ASSEMBLY OF MOTOR. 



The different parts of the motor are now complete, and it re- 
mains only to assemble these parts in their proper order. The 
diameter of the armature is such as to leave a little less than Vs 
inch clearance all around, when it is placed in the circular cham- 
ber at the bottom of the field magnet. It must be mounted in 
its bearings so as to revolve freely in the center of this space. 

To do this remove the wooden uprights at each end of the 




BRUSHES ANB 
COMMUTATOR 




METHOD 
OF MAKING 

BEARINGS 



board. Wrap around the armature enough paper, evenly wound 
on, so that the armature with the paper wrapped upon it shall 
just slip into the circular space designed for it. The paper is 
only a temporary arrangement for locating the armature in the 
center. Place it so that the ends of the armature project equally 



44 EASY ELECTRICAL EXPERIMENTS. 

from each side of the magnet. Also be sure that the com- 
mutator is on that side of the magnet which has the widest 
clearance between the magnet frame and upright piece. If all 
directions have been followed, there will be at least I inch of 
clear shaft projecting from the commutator end of the arma- 
ture, and 1% inches projecting from the other end. 

Measure the height of the shaft above the base board. In 
the middle of the two uprights, bore two holes, whose centers 
are the same height above the base as the center of the shaft. 
These holes should be fy$ inch in diameter. When these uprights 
are replaced, the end of the shaft should just come even with the 
outer surface of the upright on the commutator end, and on the 
opposite end should project at least Yz inch beyond the upright, 
to allow room for a pulley. 

Make four pieces of wood, lY inches square, J4 inch thick and 
with a smooth hole through the center just large enough to fit 
tightly upon the shaft. Slip one of these upon each end of the 
shaft. Replace the wooden uprights, allowing the shaft to pro- 
ject through the centers of the % inch holes in the uprights. 
Then slip the remaining two pieces just constructed upon the 
ends of the shaft, and push the four pieces of wood tightly 
against the uprights. Screw or clamp them there with a car- 
penter's screw clamp. Bore a Y inch hole from the top of each 
upright down into the circular chamber thus formed in the 
wooden upright. Then melt some babbitt metal, or if this can- 
not be secured, lead will do very well, and pour it through the 
% inch hole so as to fill the space between the shaft and wooden 
uprights. The object of the square pieces of wood which were 
just slipped upon the shaft is to make a little chamber in the 
upright into which the melted metal is poured as just described. 
Accordingly they must fit the shaft tightly and must fit smoothly 
against the faces of the upright. 

Now remove the uprights, remove the pieces of wood from 
the shaft, and unwrap the paper from around the armature. 
These have served their purpose, and may be thrown away. 
The bearings just made will probably fit the shaft too tightly, 



EASY ELECTRICAL EXPERIMENTS. 



45 



and should be carefully reamed out until the shaft turns very 
freely, when oiled, but not loose enough to rattle. In replacing 
the upright strips, care must be taken to put them on at the 
same end and in the same position as when the bearings were 



c 



] 




s 



End View of Motor. 

cast, as otherwise the shaft will bind. The bottom of the up- 
rights should be very smooth and square for the same reason. 
There will be a little room for the shaft to slip sidewise, if 
all dimensions are correct. At the commutator end, the latter 



46 EASY ELECTRICAL EXPERIMENTS. 

should be kept at least y 2 inch from the bearing by means of a 
brass ring of that width slipped upon the shaft. Be very sure, 
however, that this ring does not touch the commutator seg- 
ments. Failure to observe this precaution will render the motor 
useless. At the other end of the shaft a narrow ring should 
also be slipped on, so as to keep the armature from moving 
sidewise. This last ring is also very important, as it keeps the 
armature wires from striking against the bearing, and must not 
be omitted. 

The brushes which are to press upon the commutator and 
carry the current to the armature must next be made. These 
should be cut out of very thin sheet copper, very springy and 
flexible. They are about I 1 /* inches long, J4 inch wide and of the 
shape shown at S. One is attached to the upright as shown at 
A. It bears firmly against the commutator on a vertical line 
passing through the center of the shaft. The other spring of 
the same size and shape is shown at B, and presses against the 
commutator directly below the shaft, as shown by the dotted 
line. 

These springs are connected to binding posts as shown at C, 
which connects with one terminal of the field coil. The other 
terminal of the field connects to A. 

The battery to run the motor is connected to posts B and C. 
The motor should then run in the direction indicated by the 
arrow. If it does not interchange the wires which run to C and 
A from the field coils. 

The motor is designed for a maximum capacity of 5 amperes 
and eight volts. A suitable battery for running the motor will 
be described in a later paper. 



EASY ELECTRICAL EXPERIMENTS. 46a 



CHAPTER XII A 



HOW TO MAKE 1-20 HORSE POWER MOTOR. THE ARMATURE 

CORE 



This and the following chapters will deal with the construc- 
tion of a small motor designed for practical service, and yet 
capable of being constructed with tools which boys ordinarily 
possess, except in one or two instances where a little lathe w r ork 
is absolutely essential. In the construction of such a motor 
the armature, or rotating part naturally occupies our attention 
first. It is to be of the so-called drum type, consisting of a 
large number of coils of wire wound lengthwise over a cylin- 
drical core of soft iron which is held upon a shaft. 

The first thing to provide for is the shaft. It should be made 
of a piece of steel rod Y± inch in diameter, cut to a length of & l / 2 
inches. Rods of this diameter and material may be bought at 
an ordinary hardware store, and may be cut to the desired length 
by means of a file. 

Upon this shaft is to be mounted a cylinder of hard wood. 
Its outside diameter is % inch and its length is 2y 2 inches. It 
must fit the shaft very tightly so that it will not turn upon the 
shaft when the full force of the finished motor is applied to it. 
To avoid splitting the cylinder in thus forcing it tightly upon 
the shaft, it is better to make the cylinder by boring a hole 
lengthwise through a rather large block of wood, forcing the 
block upon the shaft, and then turning down the block until 
it is of the right diameter. This cylinder is shown at A in 
the figure below. It should be so placed that one end of the 
cylinder is zVa inches from the corresponding end of the shaft. 
Make two circular pieces of hard wood 3-16 inch thick, ij4 inch 
in diameter, with a ^4-inch hole in the center of each. These 



46b 



EASY ELECTRICAL EXPERIMENTS. 



pieces are to be slipped upon the shaft until they lie against 
the ends of the wooden cylinder already constructed, and are 
screwed to the latter by four flat headed brass screws $i inch 




ARMATURE CORE, FINISHED 




SECTION] THR0U6R CENTER 

long and as slim as can be secured. The heads of these screws 
should be counter sunk below the surface of the wood. There 
has now been formed a wooden spool, mounted upon a shaft, 



EASY ELECTRICAL EXPERIMENTS. 46c 

the heads of the spool being removable. Its appearance will be 
clear from an inspection of the figure. The space between the 
heads of the spool is to be filled with iron. For this purpose 
iron washers are the best to use. Procure at a hardware store 
about 40 iron washers i54 inches in external diameter with a 
hole through the center Y% inch in diameter. This is a size 
which is quite common, and the above dimensions are given 
for that reason. If, however, the size of the hole should vary- 
considerably from the above, it will do no harm provided the 
diameter of the shank of the wooden spool upon the shaft be 
altered to correspond. The outside diameter is, however, very 
important. For this reason it may be best to purchase the 
Washers first. They are to be strung on to the shank of the 
spool so as to completely fill the space between the heads of the 
spool. When the space is filled, the wooden heads can be 
screwed into place so as to clamp the washers together with 
moderate pressure. As the washers average about 1-16 inch in 
thickness, and the space to be filled is 2% inches, the number 
above mentioned will probably be needed. 

Now divide the circumference of the heads of the wooden 
spool into 12 parts, marking each division point with a pencil. 
Procure some small brads %i inches long. With a pair of pliers 
cut off the heads of these brads. Now drive them into the cir- 
cumference of the wooden discs, twelve in each head, equally 
spaced, projecting J4 inch from the spool and pointing directly 
toward the center of the shaft. The projecting brads on one end 
must lie directly in line with those upon the other end. They 
are for the purpose of holding the coils of wire which are to 
be wound upon the core. Before this is done, however, the 
core must be covered with a layer of heavy paper glued smoothly 
in place in order that the coils of wire may not by any chance 
touch the iron core. The shaft also should be wrapped around 
with a layer of stout paper for a distance of one inch from each 
end of the core. 



46d 



EASY ELECTRIC AL EXPERIMENTS. 



CHAPTER XIV 



HOW TO MAKE A 1-20 HORSE POWER MOTOR. 
ARMATURE 



WINDING THE 



In the last chapter directions were given for constructing the 
armature core. Now we will proceed to wind this core with 
the necessary coils of wire. The brads projecting radially from 
the ends of the spool are for the purpose of retaining the various 
coils in place upon the spool. Since we put twelve of these 
brads upon each end of the spool, there will be spaces between 
them for twelve coils of wire. 

Before beginning the winding of the coils be sure that the 




METHOD OF WINDING. 

iron washers in the core are completely covered with a layer 
of paper. Also be very sure that the shaft is wrapped with 
heavy paper, glued on as directed. The brass screws which 
hold the heads of the wooden spool in place should be sunk 
below the surface of the wood, so that it will be impossible for 
a wire to touch them. 

There will be needed for the armature Y^ pound of No. 18 
double cotton covered magnet wire. Place it upon a reel or 
spool upon the work bench so that the wire may easily be 



EASY ELECTRICAL EXPERIMENTS. 



46e 



unwound from it, taking care in handling the wire to keep it 
smooth and straight. Support the armature core, with its 
shaft, in front of this reel of wire, by resting the ends of the 
shaft upon two blocks with the core hanging between them, so 




SECTION OF ARMATURE. 

as to allow free access to the latter. Two or three nails driven 
into the blocks will prevent the shaft from slipping off. 

Having made these preparations, we are ready for the wind- 
ing. Begin at any one of the twelve spaces and wind the first 
coil in this space. The wire is wound lengthwise along one 
face of the core, across the other end, back along the opposite 
face of the core, across the other end and back to the starting 
point, thus passing entirely around the core lengthwise. The 
method of winding is clear from an inspection of the figure 
shown. Each of the coils when complete consists of slight 
turns of this kind. There will be just room enough between 
the projecting brads for four turns to lie side by side, so there 



46f EASY ELECTRICAL EXPERIMENTS. 

will be two layers of four turns each. These must be wound 
Tery tightly and evenly, all kinks in the wire being smoothed 
out. Provide a quantity of little leather tags cut from an old 
shoe. Number one of these B-i, and fasten it firmly to the 
^beginning end of coil No. I. When this coil is finished — that is, 
is, when the whole eight turns are evenly wound — cut it off, 
leaving about six inches for connecting, and tag this end E-i, 
signifying that this is the end of coil No. i. Then twist the 
two wires together temporarily. Proceed then to wind coil 
No. 2, tagging its ends B-2 and E-2. Coil No. 2 may be wound 
foest in the space to the right of that occupied by coil No. 1. 
Proceed in this manner with the rest of the twelve coils. 

Since each coil reaches around to the opposite side of the 
core, when six coils are wound all the spaces will have wire in 
them. But this need cause no trouble. Start to wind coil No. 7 
on top of coil No. 1, but begin on the opposite side of the core; 
that is, coil No. 7 is wound in the space where it would naturally 
fall, without any notice being taken of the fact that it is wound 
outside of No. 1. Similarly, coil No. 8 is wound over coil No. 2, 
t)ut starts on the opposite side of the core. 

Of course, where all these wires overlap on the end of the 
spool, there will be formed a large bunch of wires. But this 
will do no harm provided great care is used to prevent a bare 
wire from touching its neighbor or the shaft. If the latter is 
protected with paper, there will be no trouble. Do not, how- 
ever, allow the ends of the coils to form a bunch which ex- 
tends more than one inch from the ends of the spool. 

Twelve coils should be wound, very smoothly and evenly, 
and the ends properly tagged, so that when we come to connect 
up the coils later we can distinguish the projecting ends of one 
coil from those of its neighbors. 

If the core has been mounted upon the shaft as directed, the 
shaft will project 3 inches from one end and 2 inches from the 
other. The winding should begin at that end of the core where 
the shaft is the longest. 



EASY ELECTRICAL EXPERIMENTS. 47 



CHAP. XIII -HOW TO MAKE A SET OF TELEGRAPH IN- 
STRUMENTS 



PART ONE. 



The writer well remembers the satisfaction experienced with 
his first set of telegraph instruments, made at home and oper- 
ated by a home-made battery. Such a set can be made with 
the simplest tools and with a fair amount of mechanical ingenu- 
ity, and will work admirably. 

For material there will be needed for each instrument, a small 
quantity of pine board y% inch thick, two iron bolts 3 inches 
long and 5-16 inch in diameter with a nut on each, a small piece 
of thin sheet iron and eight ounces of No. 24 double cotton 
covered magnet wire. The bolts mentioned are the kind used 
by carriage makers and carpenters. The sheet iron can be 
obtained by putting an old tomato can into a fire until it is 
melted apart, and the tin upon its surface is all melted off. This 
leaves the iron of which the can is made free from tin, and its 
surface may be cleaned with a bit of sand paper. 

Take a piece of board 6]/ 2 inches long, 4 inches wide and Yz 
inch thick. This is to serve as a base board upon which the 
instrument is to be built. At a distance of z z A inches from one 
end, mount an upright board 4 inches long and 2^4 inches wide. 
Being as long as the base board is wide, it extends completely 
across the latter. Before screwing it to the base board, bore 
two holes in it 5-16 inch in diameter, at a height of 1 inch from 
one edge, and 1^2 inches apart. The appearance of this piece is 
shown in Fig. 1 at A. 

Procure two bolts, of the kind previously described, and of 
the size mentioned. These are shown at B in Fig. 1. The head 
end of these bolts is usually square. Cut out of a piece of sheet 



48 



EASY ELECTRICAL EXPERIMENTS. 



iron about fifteen pieces 2$4 inches long and I inch wide. Near 
each end cut a slot just wide enough to fit the end of the bolt 
just close to the head. The distance between the centers of these 
slots should be i T A inches. The cutting can be done with an 0I4 
pair of shears. There should be enough of these strips to form 
a pile about 3-16 inch high when tightly pressed together. These 
are shown at C in Fig. 1. 

Next cut out four circular pieces of wood, Y% inch thick and 
1% inches in diameter. Through the center of each cut a hole 
just large enough to fit tightly upon the iron bolts. These 



_L_ - 

I 


4" • — * 


1 


A 


|o 


O 


1 






c 



B 



Ltlju 



FIG.' I 

pieces of wood are to form the heads for the spools of wire to 
be wound upon the bolts which are to form the cores of an 
electromagnet. Their appearance is shown at D in the figure. 

Slip two of the circular wooden pieces upon one of the bolts. 
Place one of them at a distance of 3-16 inch from the head of 
the bolt. Place the other at such a distance that there will be 
V/2 inches of free space between the two. Cover the iron bolt 
between these pieces with a layer of heavy paper glued in place. 
One of the circular pieces should be kept at the proper distance 



EASY ELECTRICAL EXPERIMENTS. 



49 



from the head of the bolt by a wedge made of wood inserted 
between the head and the wooden piece. The position of the 
other circular piece can be regulated by turning the nut upon 
the bolt. Wind the space between these two pieces with 12 
layers of No. 24 double cotton covered magnet wire. Repeat 
this operation with the other bolt, thus forming two coils with 
the bolts as cores. 

The strips of iron which were cut out are to connect the bolts 
together at the end where the heads are. Remove the tem- 
porary wooden wedges and insert the strips of iron between the 
heads of the bolts and the heads of the coils. Put them in first 




y 



FIG. 2 



from one direction and then from the other, so that the 
slots will run in alternate directions. The finished magnet will 
then look like the one shown in Fig. 2. Now remove the nuts 
from the end of the bolts, using great care not to disturb the 
wooden heads of the spools, and insert the ends of the bolts 
into the holes in the upright piece first constructed. They should 
project through the piece about Y% of an inch and are clamped 
firmly in place by screwing the nuts up tight against the board. 
This will hold the coils firmly against the board, and at the same 



50 EASY ELECTRICAL EXPERIMENTS. 

time clamp the strips of iron at the rear end of the coils very 
tightly together. 

Fasten the piece of board with its attached magnets to the 
base board by screws passing up through the base board. One 
end of one coil of wire should be connected to one end of the 
other coil in such a manner that a current going around the 
coils will go around one magnet coil in a direction opposite to 
the direction in which it goes around the other. Connect the 
free ends to two binding posts. The appearance of the appara- 
tus as thus far constructed is shown in Fig. 2. In the next 
chapter we shall see how to complete the instrument. 



EASY ELECTRICAL EXPERIMENTS. 



51 



CHAP. XIV— HOW TO MAKE A SET OF TELEGRAPH IN- 
STRUMENTS. 



PART TWO. 



Having made the coils and mounted them upon the base board 
as explained in the preceding chapter, the next thing to be done 
is to make the armature, or moving part, by which we can read 
the messages. 

Cut a piece of wood of the shape shown at R in the accom- 



<£=2L 




Fig. 3, 

panying figure. It is Y% inch square, and 2}i inches long. At 
one end fasten two pieces of thin brass or iron Y% inch wide and 
Y% inch long. These should project % inch beyond the end of 
the piece of wood. Before fastening them to the wood, punch 
two small holes through them near the projecting ends. These 
pieces of metal are to serve as a sort of hinge, so that when 
a small nail is pushed through these holes, the piece of wood may 



52 EASY ELECTRICAL EXPERIMENTS. 

swing freely upon the nail. The nail is to be held by two blocks 
sciewed to the base board as shown at the left of the figure, and 
the piece is prevented from moving sidewise upon the nail by a 
small bit of wood in the center of the nail. 

A piece of iron, shown at N is next to be screwed to the piece 
of wood just described. This piece of iron should be 1-16 inch 
thick if possible, or at least should be made of a sufficient num- 
ber of thin pieces to make up a total thickness of 1-16 inch. 
Its length is 2 inches, its width Y* inch, and it is mounted at 
such a height above the base board that its center is level with 
the centers of the projecting bolts. It should be at such a dis- 
tance from the latter that there is about % inch between the iron 
strip and the bolt when the wooden piece stands vertical. 

At the center of the upright board which sustains the coils, 
fasten a block of hard wood, shown at A. This block is 1 inch 
long, 24 inch wide, and % inch thick. It should be fastened by 
means of screws and glue in the position shown. 

The piece of wood shown at H is 2 inches long, 24 inch wide, 
and Y\ inch thick at its thin end. At the other end it curves 
around at right angles on its inner side, the arm projecting down- 
ward being ]4 inch long measured outside. When screwed to 
the upright board as shown, there should be a clear space of 24 
inch between the block A and the inside vertical edge of H. The 
arm R, when vertical, should be in the center of this space. 
- Through the armature lever R, bore a hole whose center is Y& 
inch below the end of H. This hole should be large enough so 
that a brass screw 24 inch l° n g shall fit tightly in the hole; and 
be capable of adjustment by turning it one way or the other. 
Similarly, a brass screw of the same size, shown at S, is screwed 
through the wooden piece H. If difficulty is experienced in 
boring these holes without splitting the pieces, bore a very small 
hole first, and burn it out to the right size with a red hot wire. 

These screws are for the following purpose: When there is 
no current through the magnets, the lever R is held against the 
screw S by the tension of the rubber band B. When a current 
goes through the coils, the iron cores acting upon the armature 



EASY ELECTRICAL EXPERIMENTS. 53 

N draw it and the attached lever R toward the magnet, causing 
the screw T to strike against the block A. Of course, then the 
screws S and T must be adjusted so that the armature may move 
back and forth as just described. It moves through about Y% 
inch at its upper end. It is absolutely necessary that the screws 
be filed flat on the end so as to make a loud sound when they 
strike the wood. 

The rubber band mentioned is fastened to the armature by a 
hook made from a pin driven through R. The other end passes 
through a hole in the post P, and is held by a peg driven into 
the hole in the post. 



54 



EASY ELECTRICAL EXPERIMENTS. 



CHAP XV— HOW TO MAKE A SET OF TELEGRAPH IN- 
STRUMENTS. 



PART THREE. 



The instrument described in the preceding paper is for the 
purpose of ticking out the messages which come over the wire. 
These messages are sent in obedience to the hand of the oper- 




ator, who works a '"key" so-called, which is simply an instru- 
ment for opening and closing, with accuracy, an electric circuit. 
All that we shall have to do to make our set complete is to make 
this key. 

Cut out a piece of board, 4 inches long, 3 inches wide, and Y% 
inch thick. Draw a line lengthwise through the middle. On this 
line, and J4 inch from one end bore a small hole. On the under 
side of the board enlarge this hole, so that a i-inch brass screw 
may be screwed up through this hole, and its head be sunk below 
the level of the bottom of the board. File this screw off where 
it projects above the top of the board so that it projects % inch 
above the surface, and is flat on its upper end. At the other 
end of the board insert a similar screw. Also at a point half 
way between the first screw and the edge of the board, insert an- 



EASY ELECTRICAL EXPERIMENTS. 



55 



other screw in the manner described. This board is showrc 
at A in the accompanying figure. 

From a piece of sheet brass or copper cut a piece 2 inches 
long and K inch wide. Bore a hole through one end, and 
fasten this end to the board by a screw located % inch from the 
right hand edge and in the middle of that edge. This strip should 
be loose enough so that it may be moved sidewise easily. 

Make a piece of wood such as is shown at B, 5 inches long, 
and y% inches square. At one end mount a knob made by saw- 



<3 Q 


\ O SCREW 


X 1 


\ 




-Y 






! 






\ 
\ 
\ 

\ 


\ 


1 




PLAN of T vw / I 


BASE Qcrew"®/ / 



Fig. 2. 

ing a small spool in halves. At a distance of 1% inches from 
this end bore a hole large enough to take a 1 inch brass screw. 
The hole may be burned out, as described in the last paper, if no 
drill be available. The lower end of the screw should be filed 
flat. At a distance of % inches from the other end insert a 
similar screw. The distance between these screws should then. 



$6 EASY ELECTRICAL EXPERIMENTS. 

be 2^2 inches, which is the same as the distance between the 
two central screws on the base board. 

The lever B is now to be mounted between two blocks screwed 
io the base board, as shown in the figure. It should be at such 
a height that its under edge is §i inch from the base, and 
is so placed that the two screws, S and R are above the two 
screws in the base board. A stout round nail held in the up- 
right blocks, passes through the lever B. It should fit the latter 
tightly, but should be loose enough in the block so that B may 
move easily up and down. There should be no side movement 
of the lever, however. 

Take a piece of old clock spring, and soften one end by holding 
it in a flame. Punch two holes through it, and fasten it to the 
base board, underneath the lever, in such a manner that it 
presses upward on the front end of the lever, and holds the 
latter up so that the two screws S and T will not touch unless 
a pressure is applied to the knob. 

Take a piece of fine magnet wire one foot long. Strip the 
insulation from one end, and wrap it tightly around the screw 
S. Then coil it up into a spiral and, having stripped the insu- 
lation from the wire at a point 3 inches from the screw, twist 
the bare wire underneath the screw which holds the copper 
strip L in place. Finally connect the same wire to one binding 
post P. The screw S, the lever L and the binding post P are 
then connected together. Finally connect the screws T and W 
by a wire running in a groove on the under side of the board 
which runs to the second binding post Q. These connections 
are shown by dotted lines in Fig. 2. Adjust the screws S and R 
so that the lever B may move up and down about % inch. 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XVI -HOW TO WIRE AND USE A TELEGRAPH IN- 
3TRUMENT. 



PART FOUR. 



We are now ready to set up and use the instruments which 
we have made. Screw the sounder (the instrument with the 
coils) to a table so that it will give the loudest possible sound. 
Also screw the device for opening and closing the circuit to the 
table in such a position that it may be easily grasped with the 
fingers when the elbow is resting on the table. This last piece 
of apparatus is called a telrjraph key. Then wire up the set in 
accordance with the accompanying diagram. 

For a battery there will be needed two cells of "gravity" or 
"crowfoot" battery, or in place of these some home made cells, 
such as have been described in previous chapters. Join the two 
cells in series, i. e., with the zinc of one connected to the copper 
of the next. Join the copper pole of No. I to one terminal of 
the key. Join the other terminal of the key to one terminal of 
the sounder. Join the other terminal of the sounder to one side 
of the line. Join the zinc terminal of No. 2 cell to the other side 
of the line. If no line is yet constructed, simply replace it with 
a short bit of copper wire The connections given are for each 
end of the line, with the exception of the cells which should ail 
be located at one end. 

With the key up, the rubber band holding the armature of the 
sounder should be just strong enough to pull the armature against 
its back stop. When the key is pressed down, the current should 
be strong enough to pull the armature against the front stop 
with force enough to make a sharp tick. Be sure, however, that 
the metal strip which was mounted upon the base of the key, 
does not touch the screw projecting through the base board. 
Move the key up and down slowly and adjust its movement and 



58 



EASY ELECTRICAL EXPERIMENTS. 



that of the armature by means of the screws in each case. The 
armature should have enough movement to give out a loud 
sound, but it must not strike against the magnets. The key 
should move only a little, but should make and break the current 




o 

Connecting the Set. 

^perfectly. When not in use place the metal strip on the base 
•of the key upon the projecting screw. The circuit will then 
be permanently closed and should always be left in this condi- 
tion when not in use. Otherwise the person at the other end 
of the line cannot call the person at this end. 

Now as to the signals employed. The regular telegraph, or 
Morse alphabet, is made up of three characters — dots, dashes 
and spaces. By a proper combination of these all the letters 
•of the alphabet can be made. The alphabet is as shown. 

To make a dot, press the key downward with a quick, yet 
£rm motion, so timing the movement that the two ticks of the 
sounder against the front and back stops shall come almost 
together. To make a dash, hold the key down long enough to say 
"one" between the two ticks. To make the various letters, com- 
bine properly accordingly to the letter which it is desired to 
send. Remember, however, that a space means as much as a 
4ot or a dash, and be careful not to insert one where there is 



EASY ELECTRICAL EXPERIMENTS. 59 

none. Thus, there is no space between the dot and dash in 
A, and the dash should follow the dot immediately. In making 
the letter C for example, there is a space between the second 



A- — 


K 




U - 





B 


L 




V - 





C-- - 


M 




w- 





D 


N — - 




X- 





E - 


O- - 




Y- 


- - - 


F 


P 




Z- 


" - " 


G 


Q 




&- 





H 


R- -- 




. - 





I -- 


s--- 




9 





J 


T — 

Morse Telegraph Alpha 




p _ 




1 bet 







and third dots. Make the first two very close together and 
leave the shortest possible space between these and the last dot. 

The space between words is twice as long as the space be- 
tween letters. A large amount of practice is necessary in order 
to become skillful, but in time the letters will become as familiar 
to the ear as spoken words are, and the operator will not have 
to stop and think when he wishes to recall a letter. 

The instruments described will work with two cells over a 
line 200 feet long. Using more cells it can work over much 
longer distances, depending upon the quality of workmanship, 
and the condition and size of the line. The ground may be 
used for one wire, provided contact is made with pipes driven 
deep into the earth, and provided the other wire is perfectly in- 
sulated. 



6o 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XVII -HOW TO MAKE A DRY CELL. 



c 




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Of late years the so-called dry cells have come into common 
use, chiefly because of their cleanliness and portability. Ordi- 
nary liquid cells for ringing elec- 
tric bells and for similar pur- 
poses employ a stick of zinc, and 
a carbon plate, immersed in a 
solution of sal-ammoniac. Dry 
cells use the same material for 
the two poles of the cell, but in- 
stead of a liquid, use a paste 
formed by the mixing of sal- 
ammoniac and other salts, with 
water. They are not then per- 
fectly dry, in the sense that they 
contain no moisture, but only de- 
serve the name because the paste 
is thick and cannot spill as a li- 
quid would do. 

To make such a cell there will 
be required first of all, a strip of 
sheet zinc Sy 2 inches long and 6 
inches wide. Roll this up into a 
cylinder 6 inches high and 2j4 
inches in diameter. The zinc will 
overlap on the side about ¥& inch, 
and should be tightly soldered. 
Also solder a circular piece on to 
one end of the cylinder, so as to 
IA Dry Cell. completely close that end, and 

form a water-tight vessel. This piece should have its edges 
flanged, and an attempt should be made in soldering to prevent 



EASY ELECTRICAL EXPERIMENTS. 61 

the lead used in the solder from running inside the cylinder so as 
to make contact with the contents of the cylinder. For this rea- 
son, the joints should be painted on the inside with good asphalt- 
um paint. Do not, however, put the paint anywhere except at 
the joints. 

Procure next three carbon rods such as are used in arc 
lamps. Each rod should be 6 inches long and about y 2 
inch in diameter, and copper plated. Remove the cop- 
per plate from each by means of a file except for a space of 
y 2 inch from one end. Bind them together, the plated ends at 
the same end, by means of strings. Solder to the copper plate 
at the ends of carbon rods a wire, which pass around the three 
rods, making contact with each rod through the medium of the 
solder, and the ends of which project 2 inches above the rods. 

Immerse this end of the rods in a smoking hot dish of melted 
wax (either paraffine or beeswax), until the pores of the carbon 
for a space of one inch from the ends of the rods are thoroughly 
saturated with the wax. 

To make the paste take j£ lb. zinc oxide, % lb. sal-ammoniac, 
Y^ lb. plaster paris, % lb. chloride of zinc and mix them into a 
paste by adding y 2 pint of water. The first three ingredients at 
least can probably be secured even by those who have not access 
to the larger stores. In case of necessity the chloride of zinc may 
be omitted, and its place supplied by using a little more of the 
other solid ingredients. 

Insert enough paste into the bottom of the zinc cylinder to 
form a layer y 2 inch thick. Rest the end of the carbon rods up- 
on this, with the plated ends projecting from the top, and hold- 
ing the rods in the center of the cylinder, push the paste into 
the space between the rods and the cylinder, using a stick for 
the purpose. Fill the space evenly all around the carbon rods, 
until the paste is within 24 inch of the top of the dish. 

Pour over the top of the paste a wax made by melting together 
y 2 lb. rosin and 2 oz. of beeswax. This seals the cell, prevent- 
ing the contents from evaporating and spilling. Connection is 



62 EASY ELECTRICAL EXPERIMENTS. 

made with the zinc by a wire soldered to the outside of the zinc 
cylinder at the top. Connection is made with the carbon rods 
by means of the wire soldered to them. In both cases, screw con- 
nectors similar to that shown in the figure are very desirable. 

Such a cell is very useful when currents are wanted for a 
very short time, as for example, in the case of the electric bells. 
This form of cell is, however, wholly unfitted for those purposes 
where a current is desired for a considerable time, like telegraph 
work. The cell described gives an electromotive force of 1.3 
volts and will easily ring an electric bell through 50 ft. of wire. 

If carbon rods which are plated with copper cannot be secured, 
they may be plated as described in a previous chapter. Or con- 
nection may be made by twisting wires firmly about the upper 
ends of the rods. 

It will improve the working of the cell very much if the carbon 
rods are surrounded by a layer of black oxide of manganese. 
If this can be secured it should be used, although those who do 
not have access to the large cities, may find some difficulty in 
securing it. It can be ordered sent by mail from any electrical 
supply house and is not expensive. 



EASY ELECTRICAL EXPERIMENTS. 



63 



CHAP. XVIIX-HOW TO MAKE A SET OF TELEPHONE IN- 
STRUMENTS. 



PART ONE. 



On page 127 a simple telephone is described, designed to 
be used over a short line. As there described the instrument 
was designed to be used both as a receiver and as a trans- 



Cover. 
Front View, yrith 
hack removed 




I 



fport for 
carlron is shown 
dotted 2 tries 



mitten That is, a person using the instrument would talk into 
and listen to the instrument alternately, no battery being re- 
quired for its operation. Such an instrument is, however, un- 
suited for lines of much length, and the purpose of this and the 
following chapters is to describe an instrument capable of use 
over a line one mile in length, or even greater distances. 

There are three essential parts to every telephone, viz. — a 



64 EASY ELECTRICAL EXPERIMENTS. 

transmitter, a receiver and some form of signalling apparatus 
for calling. These will be described in the order named. 

To make the transmitter, make a wooden box whose length 
is 4^4 inches, whose width is zYa inches and whose depth is 
iy 2 inches, measurements being taken inside the box. This 
should be made of % inch whitewood, and one side, the cover, 
should be fastened on with screws. 

In the middle of the cover of this box. cut a circular hole 
2J4 inches in diameter. Cut out also from a separate piece of 
whitewood, a circular piece 3%. inches in diameter, with a % 
inch hole in its center. This is shown at A in the figure. On 
one side the hole is cut away so as to form a mouthpiece as 
shown in the figure. 

This piece is to be screwed to the front of the cover, exactly 
fitting over the hole cut in the cover. There is % inch margin 
left all around the hole, and this will be sufficient to hold the 
screws, if care be exercised. Before screwing it on, however, 
cut out of a piece of very thin ferrotype iron, a circular piece 
3% inches in diameter. Bore a small hole through its center, 
and bore holes near the edges so that the screws holding the 
circular piece A to the cover, can pass through the iron. Cut 
out also from a piece of very heavy cardboard, a ring, whose 
outside diameter is 3%. inches, and whose inside diameter is 
2^4 inches. Now place the circular piece of iron over the hole 
in the cover, place the pasteboard ring on top of it, next place 
the circular piece of wood on top of the ring, and clamp the 
whole firmly to the cover by four screws. The iron is to be 
the diaphragm of the transmitter. The pasteboard ring is to 
keep the circular board from touching the iron, so that the 
latter is held only at its edges. 

Make next a wooden frame shown at B. It consists of three 
pieces. Two of these, the side pieces, are each 2^i inches in 
extreme length, % of an inch in height, and 1 inch wide at the 
center. The other piece connecting these two is 1 inch wide, 
3 inches long and % inch thick. 



EASY ELECTRICAL EXPERIMENTS. 65 

Take a piece of carbon rod, such as is used in electric lamps, 
and cut out two pieces each $i inch 'long and ^2 inch in diam- 
eter. Bore half way through each piece lengthwise a very 
small hole, using a rotating drill for the purpose. If the carbon 
is held tightly in a vise, and if the boring is done very slowly, 
using a light pressure, the carbon need not be split in the 
process. At right angles to this bore another hole passing 
from one side to the other. In this drive a wooden plug. A 
section of the carbon is shown at C. Fasten one of these 
pieces of carbon to the center of the wooden frame B, by a 
screw passing through the wooden strip and into the hole in 
the carbon. Fasten the other piece of carbon to the back of 
the diaphragm in a similar manner. 

When the wooden frame B is screwed to the back of the 
cover of the box, these two pieces of carbon should lie exactly 
in line, and there should be a clear space of about }i inch be- 
tween them. Adjust them by filing until this condition is se- 
cured. 

In fastening the pieces of carbon in place, insert a piece of 
fine copper wire (about No. 30) under the end of each piece 
next to the screw, so as to make contact with the carbon. 
These wires should be about 6 inches long. 

The little space between the carbon pieces is to be filled with 
very finely powdered carbon. Pulverize a quantity of the car- 
bon rod with a hammer, until it is no coarser than fine sugar. 
Wrap around the two pieces of carbon, after they are both 
firmly in place, a small strip of thin cotton cloth. Fill the 
space between the carbon blocks with the powdered carbon, 
retaining it in place by means of the strip of cloth, which 
should be bound around the carbons with a thread. 

The two carbon blocks are now supported, the one at the 
center of the diaphragm, the other at the center of the strip 
at the back, with a % inch space between them, which is filled 
with powdered carbon. The cloth, wound around the car- 
bons, holds the powder in place, yet it does not prevent the 



66 EASY ELECTRICAL EXPERIMENTS. 

free vibration of the diaphragm and its attached carbon block. 

Connect the front carbon with a binding post on the top 
of the box, and the back carbon with a second binding post, 
by means of the wires described. Screw the cover and its 
attachment to the box, and our transmitter is complete. 



EASY ELECTRICAL EXPERIMENTS. 



6? 



CHAP. XIX —HOW TO MAKE A SET OF TELEPHONE IN- 
STRUMENTS. 



PART TWO. 



Having made the transmitter, we must next make the receiver. 
This will require the following materials : One six-inch horse- 




FRONT VIEW 

DIAPHRAGM REMOVES 

shoe magnet, one ounce of No. 36 double silk covered magnet 
wire, two No. 10 flat head iron machine screws one inch long,. 



68 EASY ELECTRICAL EXPERIMENTS. 

and a few pieces of whitewood from % inch to Yz inch in thick- 
ness. 

Cut out a piece of wood, zYz inches square, and V2 inch thick. 
Draw a line through its center parallel to two edges. Lay the 
horseshoe magnet upon this piece, with its ends parallel to the 
line just drawn, and projecting % inch beyond the line. This 
magnet is to be clamped firmly in place by a wooden cleat shown 
at H. Too much pains cannot be taken to see that the magnet 
is fixed so firmly in place that it will not work loose. For this 
reason a wooden wedge inserted between the arms of the magnet, 
and screwed to the backboard is desirable. Use only brass screws 
in this part of the apparatus. 

Having clamped the magnet in place, make next a piece of 
wood 3V2 inches square and iJ4 inches thick, with a circular 
hole cut out of its center 3 inches in diameter. It may be built 
up of two Y§ inch pieces glued together, and the hole may be 
cut out by means of a scroll saw, or by the help of a small drill. 
This piece is to be fastened to the piece upon which the magnet 
is mounted, and secured firmly in place by means of glue and 
hrads. Of course it must be cut away on the under side so as 
to fit over the magnet snugly, and also over the cleat which 
holds the magnet in place. This will make a box, square on the 
outside, but circular inside, with the poles of the magnet pro- 
jecting through one side, and resting at the center of the box. 

The coils next claim our attention. One of these is shown 
complete, and is also seen at C. They are made as follows: 
Cut out a piece of wood 1%, inches long, Y% inch thick, and Y% 
inch wide. Cut away one end for a distance of Ya inch, so that 
it is only J A inch thick. Through the center of the piece, and 
7-16 inch from the thin end, bore a hole the size of the iron 
screws first mentioned, and push one of the bolts through the 
hole, from the side that is cut away. Bevel the hole on this 
side so that the head of the screw will sink down almost level 
with the surface of the strip. Make a circular wooden piece 
26 inch in diameter, and Y% inch thick, with a hole through its 



EASY ELECTRICAL EXPERIMENTS. 69 

center just big enough to fit tightly upon the screw. The strip 
first mentioned is to form one end of a spool of wire. The cir- 
cular piece just described is to form the other end, and is ac- 
cordingly screwed on to the screw after the latter is in its place 
in the wooden strip. These pieces are shown as S and T re- 
spectively. 

The space between them is to be wound full of No. 36 double 
silk covered magnet wire. Before beginning to wind, cover the 
iron core with a layer of heavy paper, gluing it in place. Make 
two coils exactly alike, using the two iron screws for the pur- 
pose. 

The strip S is made of the shape shown in order that the coils 
may be screwed to the inside of the bottom of the box, with 
the heads of the screws resting firmly against the poles of the 
steel magnet. Their position is shown in the right hand figure. 
Be sure that they are fastened firmly in place by means of a 
screw and a little glue. Then connect the terminal of one coil 
with one terminal of the next so that a current will go around 
the second coil in direction opposite to that in which it goes 
around the first. Connect the two remaining terminals to the 
two binding posts on the back of the receiver. 

All that remains is to make the diaphragm and to secure it 
in place. It should be made from a piece of very thin ferro- 
type iron, such as photographers use. Cut out a circular piece 
2^/2 inches in diameter. Cut out also a piece of wood, 3% inches 
square, and % inch thick, with a hole through its center Y\ 
inch in diameter. Hollow out one side to form a mouthpiece 
as shown at B. Cut out a circular ring of heavy cardboard, 
whose external diameter is 3% inches, and whose internal di- 
ameter is 3 inches. 

Place the iron diaphragm over the front of the box contain- 
ing the coils. It should almost touch the ends of the iron 
screws. Adjust it so that there will be 1-32 inch between the 
ends of the screws and the diaphragm. Then place the paste- 
board ring on top of the diaphragm, put the wooden mouth- 



70 EASY ELECTRICAL EXPERIMENTS. 

piece on top of this, and screw the whole together by four 
screws at the corners.. The pasteboard ring keeps the wooden 
mouthpiece from touching the diaphragm except at the edges, 
leaving the diaphragm free to vibrate. 



EASY ELECTRICAL EXPERIMENTS. 



7i 



CHAP. XX 



—HOW TO MAKE A SET OF TELEPHONE IN- 
STRUMENTS. 



PART THREE. 



In addition to a transmitter and a receiver, we need some 
form of apparatus by means of which either party can call up 




%^ 



the other. The ordinary form of electric bell with push button 
is hardly sensitive enough, unless the line be very short, and 
the battery used very powerful. We need too, some simple de- 



72 EASY ELECTRICAL EXPERIMENTS. 

vice for cutting the battery out of service when the instru- 
ment is not in use, and for cutting the ringing device into ser- 
vice when desired. The apparatus to be described accomplishes 
these purposes, and is not difficult to make. 

Make a wooden box which is 6 inches wide, 8 inches long, 
and 4 inches deep,, measurements being taken on the inside of 
the box. It should be provided with a cover which may be 
fastened on by screws. The material used is % inch in thick- 
iiess. 

Take a piece of brass or copper rod % inch in diameter, and 
about 8% inches long. Bend one end into the form of a hook 
as shown at H. Take a piece of thin sheet copper or brass 
about 2% inches long and % inches wide. Bend this into the 
form of a V as shown at D. One arm should be about I inch 
long, and the other arm should be bent on the end so as to form 
a circular bearing which will just fit nicely on a i-inch brass 
screw. This piece of brass is to be fastened to the end of the 
brass hook just constructed. 

Bore a hole through the straight arm of the piece D, push the 
end of the brass rod through it until its end rests against the 
circular bearing, and solder the whole firmly together. The 
brass hook is then to be mounted by means of a i-inch screw 
to the back of the box, on the inside, the screw being I inch 
from the lower corner of the box. The curved end of the hook 
projects through a slot cut in the side of the box, of such a 
width that the hook may move freely up and down through a 
slot cut in the side of the box, though a distance of about one 
inch. 

The spring W is easily made from an old piece of clock spring, 
and pushes up on the hook with considerable force. The springs 
S and R are made of quite thin brass. The spring R makes 
contact with D when the hook is up, and S makes contact with 
D when the hook is down. When D is in contact with one 
spring, it must not make contact with the other. They are sup- 



EASY ELECTRICAL EXPERIMENTS. 73 

ported by the block of wood B. Be careful that the screws 
which hold one spring do not touch the screws which hold the 
other. 

At C is shown a coil of wire. Procure a piece of soft iron 
rod 4% inches long, and % inch in diameter. Mount tightly 
upon each end a circular piece of wood % inch thick, and 2 
inches square. Wind the iron rod between the pieces with a 
layer of heavy paper, and then wind the entire space full of 
No. 30 double silk covered magnet wire. About four ounces 
will be required. Then fasten the coil in its place in the upper 
left hand corner of the box. 

The spring T should be as thin and flexible as it can be 
made. Very thin copper or brass will answer. It carries at its 
outer end a small piece of iron, which serves as an armature, 
being attracted towards the coil whenever a current goes 
through the latter. The spring should be long enough so that 
its end will touch a brass screw inserted in the side of the box, 
when the armature is attracted towards the coil. When the 
armature moves away from the coil, the spring should not 
touch the brass screw just mentioned. In order to make this 
part of the apparatus as sensitive as possible, the spring T 
should be as long as possible. It is supported by the block A. 

To the sides and top of the box, fix six binding posts, in the 
positions shown. Connect the upper terminal of the coil to the 
right hand top binding post. Connect the other terminal of the 
coil to the spring S. Connect spring R to the binding post on 
the right hand side. Connect the spring T to the upper binding 
post on the left hand side. Solder a very small flexible wire to 
the end of the hook H after the latter is in place. Connect 
this wire to the left hand binding post on the top of the box. 
Connect the lower binding post on the left hand side to the 
small brass screw just below it, and this part of our apparatus 
will be complete. The cover of the box may be screwed on, 
and we will be ready next to set up the various parts of our 
telephone. 



74 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XXI 



—HOW <TO MAKE A SET OF TELEPHONE IN- 
STRUMENTS. 



PART FOUR. 



The different parts of our telephone should be supported on 
a suitable backboard which holds them firmly in place, and enables 
us to support the whole instrument on the wall. This backboard 




F.G.I Fig. *. 

should be made from a piece of ^-inch board. It should be 
about 20 inches long and io inches wide. Fasten the box con- 
taining the movable hook to the upper part of this board by- 
screws passing through the bottom of the box. Fasten the trans- 
mitter first constructed at a convenient distance below this in a 



EASY ELECTRICAL EXPERIMENTS. 75 

similar manner. There will be needed, in addition to the ap- 
paratus constructed, an ordinary electric bell, a push button such 
as is commonly used for doorbells, and about five cells of dry 
battery such as will be described in Chapter XXVIII of this 
book. 

Mount the electric bell in a convenient place near the tele- 
phone. Connect one terminal of the bell to one of the binding 
posts on the left-hand side of the box containing the hook. Con- 
nect the other terminal of the bell to one cell of dry battery. 
Connect the other terminal of the battery to the binding post 
immediately below the first one just mentioned. Mount the push 
button on the front of the telephone as shown at P, and run a 
wire from it to the upper left-hand binding post, and a wire 
from the button to another binding post screwed to the back- 
board, and shown at S. Join four cells of dry battery in series, 
and connect. one terminal of the battery to the upper right-hand 
binding post. Connect the other terminal of the battery to the 
"binding post S. Connect the binding post on the right-hand 
side of the box to the right-hand binding post on the trans- 
mitter. 

Provide now two pieces of flexible wire about three feet long 
and insulated. Connect one end of each to the binding posts on 
the receiver, and the other end of one to the binding post S, 
and the end of the other to the remaining terminal of the trans- 
mitter. This finishes our connections, and all that remains now 
is to adjust the different parts and study their action. The con- 
nections just described are indicated in Fig. i. In Fig. 2 is 
given a diagram which illustrates the principles upon which the 
apparatus works. 

First as to the adjustments necessary. The receiver will re- 
quire the least adjustment, and if made according to the direc- 
tions given, should work perfectly. The transmitter should be 
carefully examined to see if the powdered carbon is still in its 
place between the two carbon terminals. These terminals should 
be mounted with the precautions described. The terminal at- 
tached to the diaphragm should move freely with the latter. The 



76 EASY ELECTRICAL EXPERIMENTS. 

back carbon terminal should be firmly fixed in place. The hook 
should next be examined carefully to see if it moves freely up 
and down. Notice especially if it makes and breaks the circuit 
between the two contact springs as described. Examine the 
spring carrying the armature to the ringing coil described in the 
last number and adjust it so that the armature will be attracted 
towards the coil with the least possible current. Be sure that 
the armature makes contact with the screw mentioned in the 
preceding paper. 

Turning now to Fig. 2, let us see how our telephone should 
work. The line which connects our telephone with that of the 
person with whom we are talking is connected to the two bind- 
ing posts at the top. If the receiver be hung on the hook so as 
to pull the latter down there will be a circuit from H to the 
hook, to the lower contact point, to one terminal of the coil N, 
and from the coil back to K and thence to line. If a person at 
the other end of the line should connect a battery to the line the 
current would pass through the coil and would draw its arma- 
ture up, ringing the electric bell. 

Suppose, now, that the receiver be taken from the hook so 
that the latter may move upwards by reason of the spring 
previously described. Then the hook will break contact with 
the coil N and will make contact with the upper contact point. 
This will throw into circuit the transmitter T, the receiver R, 
the main battery C and the line. We are then ready for talking. 
When the telephone is not in use the receiver should always 
be hung on the hook to save the battery. 

One thing more needs to be described. The push button indi- 
cated at P connects the battery directly across the line. When 
this is pushed the current from the battery goes directly to line 
and actuating the armatures of the coils at each end, causes them 
to ring the electric bells connected in circuit with their arma- 
tures. If the line be very short and the armature of the coil N 
very delicately pivoted, then the act of removing the receiver 
from the hook at one end will ring the bell at the other end of 
the line. 



EASY ELECTRICAL EXPERIMENTS. 



Tt 



CHAP. XXII 



-THE MEASUREMENT OF RESISTANCE. 



It is very often desirable to measure the resistance of various 
pieces of electrical apparatus, such as coils, and wires of vari- 
ous kinds. It is not at all difficult to construct a piece of appa- 
ratus which is capable of measuring resistances with a consid- 
erable degree of accuracy. The material needed for the con- 
struction of this apparatus is as follows, — a piece of pine board* 
42 inches long, 8 inches wide, and % inch thick, a piece of No. 




22 German silver or iron wire about a yard long, an ordinary 
wooden yardstick, a strip of brass or copper 4 feet long, J4 
inch wide, and at least 1-32 of an inch in thickness, and five or- 
dinary binding posts. 

Cut the board to the dimensions given above, and smooth it 
off nicely with sand-paper. It is well to bevel the edges of 
the board for the sake of appearance. Near one edge of the 
board, and parallel with the edge, fasten the wooden yard-stick, 
as shown at H in Fig. 1. Three screws passing through the 
yard-stick and into the pine board will be sufficient. 

Cut off two pieces of the brass strip each 5 inches long. 
These are to be fastened to the board at the end of the yard- 
stick, and are shown in the figure at C and D. The thickness 
2i 1-32 inch given above for these strips, was chosen for the 



78 EASY ELECTRICAL EXPERIMENTS. 

reason that this thickness would be easier to work for those 
possessing few tools. If possible, however, the thickness of 
all brass strips used should be 1-16 inch. 

Now cut off another strip of brass whose length is 32 inches. 
This strip is shown at A in Fig. I, It is screwed to the board 
so that it is in line with the end of strips C and D, and there 
is a 2-inch gap at S and X, as shown. 

Put binding posts at the middle and ends of strip A, and also 
.at the rear end of strips C and D, as indicated. 

The next thing is to make the key shown at K in Fig. 1, and 




U 





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3 


/*\ /*\ 


II 

F.6. 2 




w 




| 






A 



shown enlarged in Fig. 2. The body of the key is made from 
a block of wood 2^2 inches long, 1^4 inches wide, and % inch 
thick. It is hollowed out on the under side as shown at H, 
so that it will fit snugly over the yard stick, and slide easily 
along the latter. On account of the different width and thick- 
ness of various yardsticks, it is impossible to give dimensions 
for the slot shown at H, but the amateur can easily arrange this. 

The top of the block is cut down for a distance of l /s inch 
except for a distance of Y^ inch from one end. This end is 
left higher than the rest of the block so that the spring S may 
foe fastened to the block in such a manner as to be capable of 
being moved freely up and down. In order to make it easy to 
press the spring downward, a wooden button B is screwed to 
the spring at a point just inside the end of the block. The 
spring S is made of a piece of 1-32 inch spring brass, and is 
bent over at right angles at one end as shown. The length of 
the long arm of this spring is 4 inches, and that of the short 
arm is 5-16 inch. The latter is beveled on its end to a sharp 
edge. 

Now take a piece of German silver wire of the size already 



EASY ELECTRICAL EXPERIMENTS. 79 

given, and a little longer than the yardstick. Stretch it length- 
wise over the yard-stick, drawing it very smooth and tight along 
the surface of the latter, and clamping it firmly under the brass 
strips at the end. The wire should be very smooth and straight. 
Iron wire could be used, if it is impossible to obtain anything 
else, but it will give trouble, unless it is kept very carefully 
cleaned. 

The key K when placed upon the stick, should slide very 
smoothly along the latter, and the brass spring should just clear 
the wire on the stick. 

In using the apparatus, some form of sensitive galvanometer 
must be employed. Such a galvanometer was described in the 
second chapter of this book. Another form will be described in 
a later chapter. One terminal is connected to the binding 
post at the center of strip A, and the other terminal is con- 
nected by means of a long flexible wire to the key K. 

At S is inserted a coil whose resistance is already known, 
and at X is inserted a coil or wire whose resistance we wish 
to determine. A battery of two or three cells is connected 
across from C to D as indicated at B. 

The method of using the apparatus will have to be explained 
in the following chapter. 



8o 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XXIII -THE MEASUREMENT OF RESISTANCE. 



In the last chapter we constructed a piece of apparatus for 
the measurement of resistance. This apparatus is, however, de- 
pendent for its action upon some form of sensitive galvanom- 
eter capable of responding to a very weak current. Such an in- 
strument will now be described. A side view and a front view 
is given in the accompanying figure. R is a block of wood, 

Pi 




Galvanometer" 



side 

VIEW 



3 inches square and 5^ inch thick. On this block is to be 
mounted two coils, shown at O and P. One of these, P, is 
shown complete while the other, O, is shown without the wire 
in place. To make the forms for these coils, take a block of 
wood, 1Y2 inches long and J4 inch square in cross section. Next 
make two pieces of wood, 2 inches long and 1 inch wide, one 
of the pieces being %. inch thick, the other Y§ inch thick. Glue 
these to opposite sides of the block just mentioned in such a 
manner that the block will be at the center of the pieces. One 
or two small brads will help to hold them in place. This will 



EASY ELECTRICAL EXPERIMENTS. 81 

make a small form, of which the block forms the core, and 
the two larger pieces the sides. Make two such forms. They 
are to be wound full of No. 32 double silk covered magnet wire, 
of which about 3 ounces will be required. They are then to 
be mounted, as shown in the figure, at equal distances each side 
of the center of the 3-inch block, the thinner flanges of the coil 
being turned towards the center. The distance between the 
coils is Y% inch. 

Take a very small piece of soft wood, 1 inch long and about 
Y% inch in diameter. A piece of a match will answer. Push 
through it two small sewing needles, the distance between the 
needles being % inch. If the needles split the wood, push them 
through a longer piece first, and then cut the piece down to 
the right length. 

These needles are to be magnetized by stroking them with a 
magnet. But the greatest care is necessary in the process. The 
magnets must be magnetized so that the north pole of one is di- 
rectly above the south pole of the other. To accomplish this, 
stroke the end of one needle several times with the pole of a 
strong horseshoe magnet, and then immediately stroke the end 
of the needle which is directly below the first with the other 
pole of the magnet. Magnetized in this way, there is little 
tendency for the pair of needles to point north and south, as 
in the case of ordinary magnetic needles. 

Near one edge of the baseboard, bore a hole }i inch in diam- 
eter, and fit into this hole the end of a piece of brass rod bent 
into the shape shown. The height of the top of this rod when 
bent over should be about 3K inches above the baseboard, al- 
though the exact height is not important. 

Support the needles just constructed by a very fine silk fibre, 
made by untwisting a very small fibre from a bit of silk thread. 
The finer this fibre is, the better. It can be fastened to the 
needles, and also to the brass rod by means of a bit of sealing 
wax. The lower needle should hang at the center of the space 
between the two coils. 



82 EASY ELECTRICAL EXPERIMENTS. 

Connect the two coils together so that the current will go 
around them in the same direction. Connect their free ends to 
two binding posts as shown. 

Now we are ready to make use of the instrument in the meas- 
urement of resistance. Referring now to Fig. I, on page 
yy, the galvanometer is connected to the wires indicated. 
It is then turned so that the freely suspended magnetic needles 
hang in the space between the coils and parallel to the coils. If 
it is difficult to find such a position, a small piece of iron, or a 
magnet, placed near the instrument, will bring the needles into 
the desired position. 

At S, in Fig. I, is shown a standard coil. This is made by 
coiling on a spool about 39 T A ft. of No. 24 copper wire. The 
resistance of such a piece of wire is almost exactly one ohm. 
It will do nicely as a standard. At X, in the same figure, con- 
nect any coil whose resistance we wish to determine. If now 
the key K be pressed, and its position shifted back and forth, 
there will finally be found a point where there is no deflection 
of the galvanometer. At first the deflection will probably be 
quite violent, but by beginning at one end of the stretched wire, 
and working towards the other end, a point will finally be reached 
where pressing the key will not affect the galvanometer needle 
at all. When this point is found note its position on the yard 
stick. 

Then, to find the resistance of X, multiply the length of wire 
to the right of K by the value of S (in this case one ohm), and 
divide by the length of wire to the left of K. 

In case high resistances are being measured, a high resistance 
coil must be used at S in place of the one ohm coil just de- 
scribed. Having this one ohm coil to start with, the amateur 
can easily make for himself other coils of 5 or 10 ohms "each, 
and from these still higher ones. In any case the measurement 
is the easiest made, when the resistances at S and X are the 
most nearly equal. 

As an example, take the following. Suppose a 10 ohm coil 



EASY ELECTRICAL EXPERIMENTS. 8^ 

be inserted at S, and that with an unknown coil at X, a point 
is found at II inches from the left hand end of the wire, where 
there is no deflection. Then the resistance of the unknown coil 
is found by multiplying the length to the right of K (25 inches 
in this case) by 10, and dividing by II. The result would be, 
in this case, 22 7-10 ohms. In order to apply this rule, however, 
the coils must always have the position shown, that is, S must 
be on the left-hand side of the apparatus. 



84 



EASY ELECTRICAL EXPERIMENTS. 



CHAP. XXIV-HOW TO MAKE AN ELECTROPHORUS. 



Experiments with static or "frictional" electricity are always 
interesting and instructive. Whenever a substance like seal- 
ing-wax or resin or hard rubber is rubbed with a piece of fur 
or flannel, the sealing wax, or whatever substance is used in 
place of the wax, is found to be electrified. This is shown by 
the fact that it will attract pieces of paper or light balls maxie 




The Electrophorus. 
of pith. The fur, or flannel, also becomes electrified, as every- 
one knows who is familiar with the effects produced by stroking 
a cat in the dark. 

The instrument to be described in this chapter depends upon 
effects produced in the manner just indicated. By means of 
it, sparks from a quarter to one-half an inch in length may 
be easily produced, and by means of a condenser, to be de- 
scribed later, quite brilliant effects may be obtained. 

There will be needed, first of all, a large shallow tin dish. 
The cover to a tin pail will answer nicely. If possible, a 



EASY ELECTRICAL EXPERIMENTS. 85 

cover at Teast 12 inches in diameter and 1 inch deep should be 
chosen. 

In a large iron dish melt together a mixture composed of 2 
parts resin and 1 part gum shellac. There should be enough 
of the melted mixture to nearly fill the tin cover when the 
mixture is poured into the cover. This cover, with the melted 
resin inside, is shown at P in the accompanying figure. Ii 
the resin cracks a little on cooling, or if subsequent use should 
cause cracks to occur, it can easily be re-melted and used again. 

Next make a circular wooden disc, shown at C. It should be 
about H inch smaller in diameter than the inside of the tin 
cover. It is provided with a handle at the center as shown, the 
length of the handle being about 3 inches. The edges of the 
disc should be rounded off very smooth, and the whole surface 
sandpapered. 

The entire disc is now to be covered with a smooth layer of 
tin foil. A quantity of this may easily be secured of any dealer 
in tobacco, as it is used in packing the latter. Paste enough 
pieces of the tin foil together so that two circular sheets of 
foil may be cut out, each one being one inch larger in diameter 
than the wooden disc. Glue one sheet to each side of the 
wooden disc (cutting a hole in the center of one for the han- 
dle to pass through) and smooth the foil nicely over the edges 
of the disc, so that the lower and upper layers of foil overlap 
smoothly, and are glued in place. 

The disc thus made must be supported by some form of non- 
conducting handle. The easiest way to do this is to whittle 
down the wooden handle already provided, until it fits tightly 
into the neck of a moderate sized bottle. The latter is forced 
upon the wooden handle, and in using the apparatus, the disc 
must always be lifted by means of the glass handle thus formed. 

To use the apparatus, proceed as follows: Procure a piece 
of pure wool flannel, and rub the rosin briskly with the flannel 
The rosin should become electrified, and should be capable of 
attracting small bits of paper or cloth. 

Now place the tin foil disc upon the rosin and touch the tin- 



86 EASY ELECTRICAL EXPERIMENTS. 

foil with the tip of the finger. Then remove the finger, and lift 
the tin-foil disc by means of the glass handle. Holding it by 
the glass handle, present the knuckle of the other hand to the 
tin foil, slowly bringing it nearer and nearer to the disc. When 
about a quarter of an inch away from the disc, a spark will 
jump from the disc to the hand, and if the room be dark this 
spark can be plainly seen. 

It is necessary to hold the disc by its glass handle, and the 
operator must not neglect to touch the disc in the manner de- 
scribed before lifting it from the rosin. 

The sparks thus obtained are quite small, especially in warm 
damp weather. In our next chapter we shall describe a con* 
denser for storing up a large number of charges, producing 
much more powerful effects. 



EASY ELECTRICAL EXPERIMENTS. 



87 



CHAP. XXV -HOW TO MAKE AN ELECTRIC CONDENSER. 



Any piece of apparatus which is capable of storing up electric 
charges, is generally called a "condenser." The term is hardly 
a correct one, for the action is not a condensing action in the 
ordinary sense of the word. What 
does take place, however, is the ac- 
cumulation of a multitude of very^ 
small charges, until the "condenser" 
contains a 'arge quantity of electric- 
ity. Upon discharging the condenser, 
this accumulated charge gives up its 
energy, or nearly all of it, in one 
sudden rush of charge, so that the 
effect produced is much more power- 
ful than would otherwise be the case. 
The term "accumulator" would not 
be an improper one for such a piece 
of apparatus were it not for the fact 
that this term has already been uni- 
versally applied to another and far 
different piece of electrical apparatus. 
A condenser consists essentially of 
two conductors of electricity* separ- 
ated by some good insulating sub- 
stance. Thus two sheets of tinfoil 
pasted upon opposite sides of a piece of window glass, would 
make a condenser. Or a sheet of waxed paper might be sub- 
stituted in place of the glass. The larger the sheets of tinfoil, 
the more electricity will the condenser contain, other things be- 
ing equal. Making the glass (or paper) very thin, thus bringing 
the sheets of tinfoil nearer together will also increase the capac- 
ity of the condenser. 

The form of condenser described in this article is commonly 
called a "Ley den Jar." Select a one-pint fruit jar, of as thin 




88 EASY ELECTRICAL EXPERIMENTS. 

glass as possible. Procure two or three sheets of tinfoil, each 
long enough to go completely around the glass jar, and of a 
width about equal to two-thirds the height of the jar. Paste one 
of these on the inside of the jar so as to completely line the 
latter for two-thirds of its height. The easiest way to do this is 
to first cover the inner surface of the jar with an even layer of 
mucilage. Then introduce the tinfoil, rolled upon a stick, into 
the center of the jar. Then unroll the tinfoil and press it 
smoothly into place using the stick for the purpose. The bottom 
of the jar on the inside should also be covered. Then the bot- 
tom and sides of the jar should be covered in a similar manner 
on the outside. 

Next a cover should be made for the jar of well-dried wood — 
pine will answer. It should be carefully sandpapered and shel- 
laced. Through its center insert a brass or copper rod about 
1-16 inch in diameter, and 6 inches long. It should project equal, 
distances each side of the cover. The upper end is tipped with 
a small lead ball soldered in place, and finished smooth. To the 
inside end of the rod is glued a narrow strip of tinfoil, long 
enough to reach to the bottom of the jar and make contact with 
the inner coating. 

The jar may be used in connection with the electrophorous 
described in the preceding chapter. Connect the outer coating to 
a gas or water pipe. Charge the disc of the electrophorous in 
the manner described, and bring it near to the knob on the jar. 
A spark will jump from the disc to the knob. Repeat this op- 
eration a number of times, perhaps twenty or more. By this 
time quite a charge will have accumulated. By connecting the 
outer coating and the knob by means of a wire, a comparatively 
large spark will be seen to pass between the wire and the knob. 
It is necessary in this and similar experiments that the apparatus 
be warm and perfectly free from moisture and dust. 

By making several such jars, and connecting them together, 
the effects produced are still more powerful. In such case, all 
the outer coatings are connected together and to earth, while all 
the inner coatings are connected to the disc of the electrophorous. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXVL 



HOW TO MAKE A LABORATORY STORAGE BATTERY. 



PART ONE. 



The most puzzling question which the amateur electrician has 
to solve relates to the selection of a battery suitable for general 
use in experimental work. Bichromate cells are powerful while 




FlG. f 



they last, but they are expensive to maintain and polarize quickly. 
Other forms of batteries may be purchased, but they are ex- 
pensive. The ordinary gravity or Daniell cell gives a very con- 
stant electromotive force, but on account of its high internal 
resistance it is not capable of yielding strong currents. Sec- 
ondary or storage cells are capable of delivering a very strong 
current and have a very constant electromotive force, but it is 
necessary to charge them from some other source of electricity. 
The ideal arrangement would appear to be the use of storage 



90 EASY ELECTRICAL EXPERIMENTS. 

cells in conjunction with gravity cells, the latter being used to 
charge the former. The present chapter deals with the con- 
struction and operation of a small storage cell for the use of 
amateurs. 

The cell will consist of three elements, namely, a series of lead 
plates, a solution of sulphuric acid into which the plates dip, and 
a jar for holding this solution. 

Make a tight wooden box, which is SVk inches long, 4 inches 
wide and 3 inches deep, measurements being taken on the inside 
of the box. The material for this box should be Y% inch thick, 
and the box should be put together in the best possible manner 
so as to be water-tight. It may be advisable to have the box 
made by a carpenter in order that it may be more efficiently 
constructed. It should be put together with screws and glue. 
Then immerse the box in a dish of hot paraffine wax, or bees- 
wax, leaving it there for at least one hour. «If only a little wax 
is available, a shallow pan may be used and one side of the box 
immersed at a time. But extreme care should be taken to see 
that the hot wax penetrates to every fibre of the wood and fills 
up all corners and cracks. This box is to contain the acid, hence 
the necessity for the careful boiling in the wax. 

Next we will make the lead plates for the cell. At a hardware 
store procure enough sheet lead to make nine plates of the size 
and shape shown in Fig. 1. After the plates are cut out each one 
is to be bent double at the point indicated by the dotted line. Be- 
fore doing this, however, bore each plate as full of J^-inch holes 
as you can without weakening the plate. The plate is then 
doubled in the middle and has the shape shown at the right in 
Fig. 1, there being a space of ]4 inch between the two sides of 
the bent plate. It may be well to avoid boring holes near the 
point where the plate is to be bent, to avoid weakening at that 
point. 

Having prepared the nine plates in the manner above described, 
procure at a paint shop about two pounds of red lead and the 
same weight of litharge. These are materials used commonly 



EASY ELECTRICAL EXPERIMENTS. gi 

by painters. In a glass dish mix a stiff paste, made by adding 
sulphuric acid to water in the proportion of i part of acid to 20 
parts of water, and then adding red lead so as to make a very 
stiff mixture. Select four of the lead plates and fill the space in 
the interior of each full of this paste. It will probably be neces- 
sary to solder the plate together at the top where the two edges 
meet. 

In the remaining five plates place a paste made up from lith- 
arge and sulphuric acid in the manner just described. Then set 
the plates aside to dry. 

After the plates are dry they are to be assembled. Make six- 
teen wooden strips 3 inches long, Y% inch thick and Y% inch wide. 
Boil them thoroughly in melted paraffine wax; also make four 
pieces % inch wide, 7-16 inch thick and 3 inches long, paraffined 
as just described. These are for separating the plates and for 
holding them in place. 



92 EASY ELECTRICAL EXPERIMENTS, 

CHAPTER XXVII. 



HOW TO MAKE A LABORATORY STORAGE BATTERY. 



PART TWO. 



In the preceding chapter directions were given for con- 
structing the separate parts of a storage cell. Begin- 
ning with a negative plate (one which contains litharge) place 
it in the box, with the longer lug projecting from the left 
hand side. Next insert a positive plate (one which contains red 
lead) with its longer lug projecting on the right hand side. The 



^ 




7: 


I J 
■" 1 II 


A B 
— l 1 — f- 

— 1 i-t 

-1 ■ r-H 

1 II. 






-i r-r 1 

-i r-Y 

-i i— r 

i i i: 




* 


V 



Plan View of Storage Cell. 

two plates should be separated by two of the small strips of 
paraffined wood, these strips being inserted vertically at each 
end. Next insert a negative plate, and then another positive, and 
so on, the plates being alternately positive and negative. All 
the negative plates should have their longer lugs on the left, 



EASY ELECTRICAL EXPERIMENTS. 



93 



and all the positive plates should have the longer lug on the 
right. Since there are five negative plates and only four posi- 
tives, the outside plates will be negative. The plates should not 
touch each other at any point. 

Next insert the heavier strips of paraffined wood on each side 
of the plates between the plates and the box, as shown at A 
and B. These strips should wedge the whole cell firmly together, 



GRAVITY CELLS 

■»■-- HJ 



■®i- 




STORAGE 

CELL.^ 



Fig. Z. 



so as to prevent the wooden strips from floating when the cell 
is filled with acid. Yet care must be exercised not to spring 
the sides of the box, causing it to leak. 

Solder a strip of lead along one end, connecting all the nega- 
tive plates together. Do the same at the other end with the 
positive plates. 

When ready for charging, the cell is to be filled with a solu- 
tion made by slowly pouring sulphuric acid into water, the 
proportion being one part of the acid to twelve parts of water. 

In order to charge the cell, four gravity cells will be required. 
The method of connection is shown in Fig. 2. The gravity cells 
are joined in series, and the positive pole of the storage cell is 
connected to the copper terminal of the group of gravity cells, 
and the negative pole to the zinc terminal. There must be no 



m EASY ELECTRICAL EXPERIMENTS. 

mistake about this, for a reversal of current through the storage 
cell will spoil the latter. 

The wires designated by the letters H and K are supposed 
to lead to a motor or any other device for making use of the 
electric current. 

The operation of the apparatus is as follows : When no cur- 
rent is being taken through the wires H and K, current flows 
from the positive terminal of the group of gravity batteries into 
the storage cell. In its passage through the acid in the latter, 
it decomposes the acid, and the lead plates are attacked and 
changed. The red lead in the positive plate is converted into 
a brown mass, while the litharge upon the negative plate is 
converted into metallic lead. Of course, it takes time to do this, 
particularly when the cell is first set up. At first the current 
should be allowed to flow uninterruptedly for one week without 
any current being taken from the cell. 

Suppose, now, it is desired to use the cell, after it is charged. 
Connection is made at the wires H and K, and without discon- 
necting the gravity batteries a strong current can be taken from 
the cells. Most of the current will be furnished by the storage 
cell, but a little of it will come from the gravity batteries, the 
latter being thus made to do continual duty. 

It is always necessary to remember that no more energy can 
be taken out of a storage cell than is put in. For example, if 
Yat ampere flows into the storage cell for 20 hours, the cell would 
have received a charge of 5 ampere hours. Now, if the cell 
were perfect, we could take out from it just 5 ampere-hours of 
work. That is, we would take out 5 amperes for one hour, or 
2, amperes for 2j4 hours, or one ampere for 5 hours, and so on. 
But no cell is perfect, and we can never take out as much as 
we put in. As a matter of fact, the present cell, if pushed to 
its limit, ought to give a capacity of 8 ampere-hours when dis- 
charging at a rate of i^4 amperes, or 6 ampere-hours when dis- 
charging at the rate of 1*4 amperes. 



EASY ELECTRICAL EXPERIMENTS. 



95 



CHAPTER XXVIII. 



HOW TO MAKE AN ELECTRIC BELL. 



PART ONE. 



An electric bell is not a hard thing to construct, and it is 
often of great service about the laboratory of an amateur. 
Certainly the time and money spent will be repaid by the more 







N 




Fic. I 



intimate knowledge of this useful piece of apparatus, which will 
be gained through constructing it. 

Take a piece of pine board 2>Va inches wide, 5 inches long and 
y 2 inch thick. Cut away one end so that it has the shape shown 
in Fig. 1. The necessary dimensions are there given. Upon this 
board mount two wooden blocks shown at A and B. The for- 



96 EASY ELECTRICAL EXPERIMENTS. 

mer of these blocks is % inch long, %i inch wide and H inch 
thick. The latter is Ji inch long, % inch wide and y 2 inch thick. 
Fasten them to the board by screws in the positions indicated 
by the dimension lines. At the top place two small binding 
posts, as close to the edge as possible. Sandpaper the whole 
very smooth, and give it a coat of cherry or other suitable 
stain. 

Next take a piece of ordinary sheet iron, such as is used for 
stove pipes, and cut out four pieces, 1^2 inches long and ij4 
inches wide. Clamp these four pieces in a vise with their edges 
even, and with the jaws of the vise lengthwise along the strips. 
Then with a hammer bend the strips over at right angles, as 
shown at F, Fig. 1. The portion of the strips held in the vise 
should be % inch wide. With a pair of heavy shears cut off 
their edges even where they have been bent. Bore, or punch 
two holes in each of the flat faces of these right angled strips, 
the holes being Y% inch apart and on the center line of the 
faces of the strip. 

Procure at a hardware store two round h«ad iron machine 
screws, ij4 inches long and about 3-16 inch in diameter. The 
size known as No. 14 is about this size. Each should be fitted 
with a nut. 

Make four very heavy cardboard washers about % inch in 
diameter with a hole in the center just big enough to slip upon 
the screws. Put two washers upon each screw, one being close 
against the head, the other at a distance of 1 inch from the 
first. Put the screw end of the screws through two of the holes 
in the right angled strips, as shown at C and D, Fig. 1. Now 
wind the space between the pieces of cardboard with three or 
four layers of heavy paper, cut into strips just wide enough 
to fill the space between the pasteboard washers, glueing it in 
place. The strips which were bent at right angles thus serve 
as a support for the screws when the strip is screwed in place 
upon the backboard (Fig. 2). Also, because they are made of 
iron, they serve to connect the two screws magnetically. 



EASY ELECTRICAL EXPERIMENTS. 



97 



Upon each screw, in the space just described, wind about 50 
feet of No. 26 double cotton 
covered magnet wire. This 
ought to fill the space quite full. 
Connect the two coils together 
in the ordinary manner, so that 
a current going around the coils 
will trace out an imaginary let- 
ter S, going around one coil in 
a direction opposite to that in 
the other coil. 

At H, Figs. 1 and 2, is shown 
an armature built up by solder- 
ing together three pieces of 
tinned iron cut from an old can. 
These strips are iVs inches long 
and H inch wide. To one end 
is soldered a wire 2^2 inches 
long, provided with a small lead 
ball at its outer end. 

To the other end of the tinned iron strips is soldered a strip 
of very thin hammered brass, shown at K. This strip is 2$i 
inches long. It projects above the tinned strips by % of an 
inch, and its lower end is cut narrow and bent out as shown 
at H. 

If difficulty is experienced in attaching this to the strips, a 
small copper rivet driven through both, may help matters. At 
any rate its lower end should be bent out as shown, so as to 
rest against the screw S inserted through the block of wood B. 

In our next chapter we shall see how to complete the bell 
and to wire it up. 




98 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXIX. 



HOW TO MAKE AN ELECTRIC BELL. 



PART TWO. 



Having followed the directions given in the last chapter, the 
next thing is to mount the different parts of the bell in their 
proper places. For a bell, the amateur may have to dismantle 
an old alarm clock, the gongs upon these clocks answering ad- 
mirably for the purpose. Sleigh-bells are sometimes made of 
the proper shape, or a suitable bell may be purchased at small 
cost. To mount the gong, fasten a stout wooden post in the 



€ 



PUSH IBUTTON 

L 



BATTERY 



Fl(J.. J 




€ 



3> 



Fi6.:2 



center of the rounded end of the base board, the post being JH$ 
inch in diameter and fastened to the board by a screw passing 
through the board and into the post. The post should be of 
such length that when the bell is placed with its center upon 
the center of the post, the edge of the gong is % inch from 



EASY ELECTRICAL EXPERIMENTS. 99 

the base board. Fasten the gong in place by means of a screw 
passing through the bell and into the post. 

Referring to the diagram given in the last chapter, the spring 
K is fastened to the block A by two screws. The strip F is- 
screwed to the board at such a distance that the ends of the 
bolts lie very close to the strip H when the spring is against 
the screw S. Under these conditions, with the spring K pull- 
ing the armature away from the magnets with considerable 
force, the wire carrying the lead ball should be bent so that the. 
ball is about ^ inch from the bell. One end of the coil of wire 
upon the spools is connected to a binding post at the top. 
The other end of the coil is connected to the spring K. The 
screw S is connected to the remaining binding post by a wire- 
twisted firmly about it and soldered in place. 

The different parts of the bell are now in place, and the bell 
is ready to work, except for adjusting. See that K presses- 
firmly against S so as to make a firm contact. The armature 
H should then be about 1-16 inch from the lower limb of the 
magnet, and 1-32 inch from the upper end. Adjust the position 
of F until this is attained. 

If a current should enter the bell at the upper left hand 
binding post, it would traverse first the coils surrounding the 
iron cores, thence to the spring K, to the screw S and back 
to the right hand post. 

The iron cores become magnetized, and draw the armature 
H with its attached spring K, to the left. This breaks the cir- 
cuit at S (if the bell is properly adjusted) and the iron cores 
lose their attraction for the armature, allowing the spring K 
to fly back against the screw S. This completes the circuit 
again, causing the armature to be attracted again. This is re- 
peated very rapidly, the ball striking against trie bell at each 
movement. 

It is a mistake to make the spring K too weak, as this causes 
the hammer to move slowly and with little life. At each mo- 
tion of the armature toward the magnets, the armature should 
barely touch the iron cores, before the ball strikes the belL. 



ioo EASY ELECTRICAL EXPERIMENTS. 

This gives a clear tone to the bell. Of course a brass or iron 
ball is better than a lead ball upon the wire N, but some 
amateurs cannot easily procure a brass ball, while any one 
can easily make a lead ball. 

When it comes to wiring up the bell, the diagram on page 
98 may be of help. The push button had better be bought 
at an electrical supply house. For a short line one cell of 
battery should be sufficient. Fig. 1 shows how to wire the 
circuit using one push button. Fig. 2 shows how to wire for 
two push buttons. A home-made battery may be made from 
a quart fruit can, a zinc rod and four carbon rods. The latter 
are tied together and a wire is twisted around them at the top 
forming one plate of the battery. The zinc rod forms the other 
plate. The two plates dip into a strong solution of sal-ammo- 
niac contained in the jar. Such a battery is not serviceable, 
however, except for short experiiments. 

After the bell is in working order, it is well to make a 
small box to serve as a cover for the working parts of the in- 
strument. This, of course, must slip on over all parts except 
the bell, a slot being cut in the lower side to allow the wire N 
to pass through. This box may be made of pine, sandpapered 
smooth and stained with cherry or mahogany stain. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXX. 



HOW TO MAKE A RHEOSTAT. 



PART ONE. 



101 



Electrical conductors, because of an inherent property called 
resistance, have the power of limiting the value of an electric 



B 



til 



~->* 



|'" m * ^r\^C\ m ^ v *x i"^ ■ ^ ■^ l ^i^ k ^ T V*^ 




Fig. i. 
current. The greater the resistance in an electric circuit, the less 
the current, other things being equal. For this reason, resistances 
are made use of to control the strength of electric currents. 



102 EASY ELECTRICAL EXPERIMENTS. 

When a resistance is so arranged that its value can be easily and 
quickly altered, it is called a rheostat. 

A very convenient method of arranging such a rheostat is 
shown in the cut on page 101. It consists of three essen- 
tial parts — a wooden frame, consisting of two end pieces E and F > 
supported by wooden pillars N and P, 32 coils of iron wire shown 
at R, which furnish, the necessary resistance, and a dial at the 
top to which these resistances are connected, so that any desired 
number of the 32 coils may be connected into circuit. 

To make the wooden frame-work, take two pieces of whitewood 
or pine, 9 inches square, and % inch thick. Also make four 
wooden rods 1 inch in diameter and 9 inches long. Near the 
corner of each of the square pieces bore a hole, whose center is 
one inch from each edge. The hole is J4 inch in diameter. Cut 
down each end of the wooden rods to a diameter of % inch for a 
distance of % inch from the end, thus forming a shoulder so that 
the square blocks of wood may be tightly slipped on to the rods, 
forming a framework which will support the whole apparatus. 
Make all joints to fit tightly, and sandpaper the whole off 
smoothly, and fasten the whole together with screws as shown. 

From a piece of sheet copper 1-16 inch thick, cut out a ring 
whose outside diameter is 7^4 inches, and whose inside diameter 
is 454 inches. The cutting can be done with a pair of tinsmith's 
shears. Draw lines upon this ring with the sharp point of a 
knife, dividing it into sixteen equal parts. With a small drill 
bore two holes in each of the sections, these holes being % inch 
from the outer edge of the ring. With a hack saw, or the edge 
of a thin file, cut the ring into sixteen sections along the lines 
previously drawn. During this process, the ring should be held 
firmly to an old piece of board, by a % inch screw passing 
through each of the thirty-two holes in the ring. The piece of 
board may be thrown away after it has been used. 

On the top of the wooden frame first constructed, draw a circle 
7^4 inches in diameter, its center being at the center of the top. 
Divide it by pencil lines into sixteen parts, and with this circle 
as a guide, transfer the sixteen copper sections from the old piece 



EASY ELECTRICAL EXPERIMENTS. 103 

of board to the top of the rheostat, arranging them symmetrically 
around the center. Be very sure that they do not touch each 
other, and that they lie smoothly and firmly in place. It may 
be necessary to file their edges a little in order to make them fit 
into each other well without touching. 

In the center of the top bore a % inch hole. Procure a ^ inch 
stove bolt, zVz inches long, with a flat head. It should have two 
nuts, so that it may be clamped in position in the hole just bored, 
one nut being on the upper surface of the top of the rheostat, 
the other on the lower surface. 

Make a wooden knob shown at A, 3 inches in diameter, with a 
hole through its. center which will allow it to just turn freely 
upon the stove-bolt, the hole being countersunk at the top to 
receive the head of the bolt. To the under side of this knob 
fasten a strip of spring brass shown at B, which is 54 inch wide, 
1-16 inch thick, and about 4^ inches long. It has a hole bored 
through one end at a distance of y& inch from that end, the hole 
being Y% inch in diameter. The bolt is then slipped through the 
knob, the spring is slipped over the bolt, and then the spring is 
securely fastened to the knob by three flat head brass screws. 

The bolt with the knob in place is then secured to the top of 
the rheostat, at such a height that the spring will bear firmly 
upon the copper sectors already in place. The knob with its 
attached spring should then turn freely upon the bolt, so that 
the spring may touch any one of the copper sectors. 

There should be inserted between the spring and the upper nut 
on the bolt, two thin washers made of spring brass. These 
washers should be bent slightly so as to exact a pressure between 
the spring and the nut, keeping them always in contact. These 
washers are very important, and should not be omitted. 



104 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXXI. 



HOW TO MAKE A RHEOSTAT. 



PART TWO. 



Having completed the wooden framework of the rheostat, 
we will next turn our attention to the coils of wire which are 
to make up the necessary resistance. Procure about 350 feet 
of No. 18 annealed iron wire. Take an iron rod Y% inch in 
diameter, and wind tightly and evenly upon it a coil of the 
iron wire, winding on enough to make a coil 5 inches long. 



nnn 




Fig. 2. 

Cut off the wire, leaving 3 inches projecting from each end. 
Remove the coil from the iron rod, and there will be found 
a spiral of wire, about */2 inch in diameter and 5 inches long. 
Make 32 such coils. The wire should be very soft, with a very 
little tendency to spring after being bent. If necessary, the 
coil may be heated by means of a spirit lamp while in posi- 
tion upon the iron rod. 
Now fasten the end of one coil to the inside of the bottom 



EASY ELECTRICAL EXPERIMENTS, 



105 



of the wooden framework, at a distance of 4 inches from the 
center, by means of a double pointed tack driven tightly into 
the wood. This tack should grip the wire close to the coil, so 
that the loose end of the wire may project from the rheostat, 
to make one terminal of the apparatus. Pass the other end 
of the coil upward through a small hole close to one of the 
copper sectors, and clamp the loose end of the wire under the 




Fig. 3. 

screw of one section. The coil should be drawn tightly against 
the upper board, as this draws the spirals of the coil apart and 
prevents their touching each other. 

At a distance of ¥% inch from the first hole just bored, bore 
another, and through this pass the upper end of another coil 
of wire, securing it to the same sector of copper as the first 
coil. Fasten the lower end of this coil to the bottom board, 
in the same way as the first was fastened. However, when the 
third coil is put in place, the lower end of the second coil is 



io6 EASY ELECTRICAL EXPERIMENTS. 

firmly connected to the lower end of the third, by means of a 
double pointed tack, drawn firmly over the two wires. The 
upper end of the third coil is connected to the second copper 
sector, and the upper end of the spiral number four is con- 
nected to the same sector. 

Proceed in this manner with the whole 32 coils, arranging 
them in a circle. When the lower end of coil 32 is fastened 
to the board, cut it off short, without connecting it to any other 
coil. A diagram showing the principle of the method of con- 
nection is given in Fig. 2. It will be seen that the upper point 
of junction of two coils is connected to a copper sector, while 
the lower connection of two coils is made by means of a double 
pointed tack. The coils should not touch each other, except * 
at the ends. 

The beginning of the first coil, which was left long, forms 
one terminal of the rheostat. The handle forms the other 
terminal. Accordingly, an insulated wire about 8 inches long 
is bared at the ends, and one end is bent around the bolt at 
the center, and firmly clamped between the lower nut and the 
upper board. A copper washer should be inserted between the 
wire and the board. The other end of this wire is left pro- 
jecting from the rheostat, and is provided with a connector, as 
shown in the preceding chapter. This wire should be secured 
by a double pointed tack to the framework, but must not touch 
the coils on any account. 

By turning the wooden knob more or less coils may be placed 
in circuit, thus varying the resistance between the two terminals. 

Of course, wood is not a very safe material to use in such 3 
piece of apparatus, because of the liability of the wires to over- 
heat. But for an amateur who deals with small currents, the 
apparatus above described is very useful. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXXII. 



107 



HOW TO DO ELECTRO-PLATING AT HOME. 



PART ONE. 



Electro-plating is the art of covering metallic bodies with a 
thin coating of some other metal by the aid of the electric cur- 
rent. 

The process may be explained as follows : Imagine two metal 
plates dipping into a solution containing some metallic salt 
If a current be sent through the solution, passing from one plate 




to the other, the solution will be broken up by the action of the 
current, and a portion of the metal formerly held in solution 
will be deposited upon the plate where the current leaves the 
liquid. Thus if a copper and lead plate dip into a solution of 
copper sulphate, and an electric current be sent through the 
solution from the copper to the lead plate, copper will be taken 
through the solution, and deposited upon the lead plate. 

The process outlined above appears simple, but in practice 
several points must be looked after. First, the article to be 
plated must, for the sake of appearance, be rendered smooth 
and free from scratches, for every line on its surface will be 



108 EASY ELECTRICAL EXPERIMENTS. 

faithfully brought out in the deposit. Next, the surface of the 
article to be plated must be clean. This is necessary, because 
otherwise the deposit will scale off. By clean, is meant chemi- 
cally clean, — that is there must be no trace of grease or foreign 
substance upon its surface. Even the slight film which would 
result from touching an article with the fingers will ruin the 
deposit. Next, it is necessary to secure an even deposit free 
from streaks and blotches. And finally, the finished article 
must be polished, as deposits as they come from the plating 
bath are rarely bright in appearance, but are dull. We will now 
take up these processes in detail as applied to copper, silver 
and nickel plating. The amateur is strongly advised to begin 
with copper plating, as the cost is comparatively slight, and 
copper solutions are much easier to work. 

In the discussion which follows, it is assumed that the articles 
to be plated are fairly clean and smooth to start with. If not, 
the ordinary use of file, emery paper, and the finest crocus paper, 
should make them so. It will also be assumed that the reader 
has only his hands to work with, although a rotating polisher 
driven by foot power is almost a necessity for extensive work. 

Assuming that the article to be plated has been treated as 
hinted above, until its surface is smooth, the next thing is to 
prepare a bath, which will render its surface chemically clean. If 
the article is of copper, brass, steel, or iron, make up a solu- 
tion by mixing together two quarts of water, y 2 pint (8 ounces) 
of sulphuric acid, and J^ ounce each of nitric and hydrochloric 
acids. Be very careful in handling these acids as they will de- 
stroy everything they touch, when in the concentrated state. 
Be sure to pour the acids into the water, when mixing, and 
not the reverse. Put this solution into two glass fruit jars, 
and label them "Pickling Solution." 

For the sake of definiteness, let us assume that the article 
to be plated is of lead or pewter, and that it is to be copper plated. 
Prepare in a large open glass jar, a solution of copper sulphate 
(blue vitriol), in the proportion of one pound of the sulphate 
to 2}4 quarts of water, with 4 ounces of sulphuric acid added 



EASY ELECTRICAL EXPERIMENTS. iog 

after the crystals are dissolved. Procure a sheet of clean copper 
about four inches square, and punch two holes at two adjacent 
corners. The holes are to receive two small copper wires by 
which the plate is to be hung in the solution. Across the top 
of the jar containing the solution, lay a brass or copper rod, 
and suspend the plate from it by two copper wires, so that the 
plate hangs immersed in the solution, and close to one side of 
the jar. 

For battery power to do the plating, perhaps the amateur 
can do no better than to use two freshly prepared gravity bat- 
teries, connected in series. Connect the copper pole of this bat- 
tery, to the rod which supports the copper plate in the solu- 
tion. Lay another rod across the top of the jar, and connect 
the zinc pole of the battery to this rod. The rod serves as sup- 
port for the articles to be plated. 

Having followed these directions we are ready for plating. 
The connections are shown in the accompanying figure, where 
for the sake of clearness, only one cell of gravity battery is 
shown. Attach a copper wire to the article to be plated, by 
passing it through any hole that may be in the article. If there- 
are no holes, try to fasten the wire to some unimportant part, 
such as the bottom, for where the wire touches the article there 
will be no deposit of copper. Then, holding the article by the 
wire, immerse it in one jar of the pickling solution. It should 
be left there for two or three minutes, and then transferred 
to the second jar. After remaining there for the same length 
of time, lift it out by the wire, taking care rot to touch it with 
the fingers. Rinse it in a jar of fresh water, and immediately 
transfer it to the plating bath, hanging it from the rod con- 
nected with the zinc pole of the battery. 

This is indicated by A in the figure on page 107. As soon 
as the article is hung from the wire, current begins to pass, 
and copper will be deposited upon the article. The length of 
time required to secure a good deposit will vary with the size 
of the article, condition of batteries, etc., but one hour ought 
to give deposit in most cases, under the conditions indicated. As 



no EASY ELECTRICAL EXPERIMENTS. 

many articles can be plated at the same time, as can be hung 
from the rod A. They should be turned around now and then, 
so as to present different sides toward the plate P, as the side 
nearer the plate will receive the heavier deposit. The greater 
the distance between the plate and the articles, the less will be 
the difference between the deposits upon the two sides. In 
our next chapter, we will see how to treat the finished article, 
and how to do nickel and silver plating. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XXXIII. 



in 



HOW TO DO ELECTRO-PLATING AT HOME. 



PART TWO. 



If the reader has attempted to do copper plating according to 
the directions given in the last chapter, he has at least gained 
an idea as to the methods employed to obtain a good deposit 
of any metal. The solution described will not work satisfac- 
torily upon articles made of 
zinc or iron. For these met- 
als, a solution of cyanide of 
copper is necessary, but the 
writer has refrained from de- 
scribing this solution because 
it is composed of one of the 
most deadly poisons known. 
Those who desire to learn of 
this solution are referred to 
any of the numerous good 
works on the subject. 

Nickel plating will have 
more attraction for most read- 
Home Made Battery. ers, and the method of secur- 
ing good results with this metal will now be described. The 
salt of nickel, with which the best results can be secured, is the 
double sulphate of nickel and ammonium. This salt is commonly 
used by nickel platers, and there should be no difficulty in pro- 
curing it. Dealers in plater's supplies also supply plates of 
nickel, one of which should be secured about 3 inches square 
and %. inch thick. 

The solution is easily made up by dissolving % pound of the 
double sulphate to one gallon of water. The water should be 




ii2 EASY ELECTRICAL EXPERIMENTS. 

quite hot in making up the solution, but should not be used 
until cold. A tablespoonful of ammonia should be added before 
starting to work the solution, and every now and then, while 
working, a small quantity of ammonia, say H teaspoonful- 
should be added. 

The articles to be plated should be cleaned and polished as 
before described and dipped in a cleansing solution just before 
immersion in the plating bath. If of copper, German silver, 
brass or iron, the article should be dipped in the pickling solu- 
tion described in the last chapter. If made of tin, lead or pew- 
ter, a cleansing solution made by dissolving J4 pound of potash 
(bought at any grocer's) in one quart of water. This solution 
should not be allowed to touch the fingers or the clothing. 

For battery power, we need something more powerful than 
the two Gravity cells described in the last chapter. Four Grav- 
ity cells will give electromotive force enough, but the current 
will be so small that the deposits will be extremely slow. Two 
or three Bunsen or Bichromate batteries should preferably be 
used, joined in series. Nickel plating requires much more power 
than copper plating, and rather large cells should be used. 

Let us sum up, then, the process of nickel plating: Smooth 
and polish the articles with fine emery paper or crocus paper 
for a finishing touch, hang them by a small copper wire in one 
of the two cleansing solutions already described, rinse them in 
clear water, without allowing them to touch the fingers or other 
bodies and hang them from the proper terminal of the plating 
bath, in the solution of nickel and ammonium which has been 
described. 

The piece of nickel three inches square, already mentioned, is 
hung from the other pole of the plating bath, in place of the 
copper plate used for copper plating. It should br hung up by 
one corner, by a copper wire, but this wire must not dip into 
the solution. The article to be plated should be kept in motion, 
and if there are projecting parts upon it, these should not be 



EASY ELECTRICAL EXPERIMENTS. 113 

too near the nickel plate. Failure to observe these precautions 
may result in a "burned" deposit. 

Whatever battery is used, care must be taken to connect the 
article to be plated to the zinc pole of the battery, the square 
piece of nickel being hung from the rod connecting with the 
other pole. 

The author recently constructed a cell which appeared to give 
excellent results for this line of work. Procure about a dozen 
electric light carbons about eight inches long, and three zinc 
rods. Procure a glass jar about six inches deep and six inches 
in diameter. Having removed all copper from the carbons, ar- 
range them in a circle which will just fit the jar, thrusting them 
through a piece of pine board Vi inch thick. In the center of 
the board mount the three zinc rods. A wire twisted around 
the carbon rods forms one pole of the battery. Another wire 
connecting with the three zinc rods forms the other poieo For 
a solution dissolve y 2 pound of potash in two quarts of water. 

Two of these cells in series ought to give excellent results. 

In our next paper we shall study the matter of nickel plating 
further, and also take up silver plating. 



"4 



EASY ELECTRICAL EXPERIMENTS, 
CHAPTER XXXIV. 



HOW TO DO ELECTRO-PLATING AT HOME. 



PART THREE. 



When a body which has been nickel plated comes from the 
plating bath, it does not have the brilliant appearance so com- 
mon to nickel plated articles. This brilliant appearance is only- 
secured by careful polishing. Sometimes, too, the deposit ■ is 
marred with blotches and "burned" spots. This is caused by 




Fig, I. 



too strong a current, or by leaving the articles immersed too 
long, or perhaps by allowing one portion of the article to re- 
main too near the immersed plate of nickel. 

The process of polishing is quite easy, if the plater be pro- 
vided with a polishing lathe, or with any suitably mounted pol- 
ishing wheel, driven by foot power or otherwise. The polishing 
brush shown in Fig. i is commonly made of bristles, mounted 



EASY ELECTRICAL EXPERIMENTS. rrs 

in a suitable hub, so as to revolve at a high rate of speed, The 
work to be polished is held against this revolving brush. Often r 
too, a polisher, or "buffer," is made by clamping upon a spindle 
a large number of circular discs cut from muslin or canvas, or 
thin leather. When revolved at a high rate of speed, the discs 
which ordinarily are soft and yielding, stand out stiffly be- 
cause of centrifugal force, making a stiff wheel against which 
the work is held. 

To aid in the polishing various compounds may be applied 
to the surface of the revolving buffer. These are usually called 
by the general name of "rouge." They may be bought in sticks 
at dealers in plating supplies. There are hard and soft rouges r 
for coarse and for delicate work, as well as dry rouges and 
greasy rouges. 

But the amateur without special tools will have to polish the 
articles as best he can by hand, unless he can improvise a lathe. 
A great deal can be done with a piece of soft canton flannel 
upon which rouge or whiting has been rubbed. Both these sub- 
stances are common in the market under the name of "silver 
polishes." Begin with a coarse rouge, and after the roughest 
part of the work is done, use a finer rouge. Then, using a 
clean piece of flannel, rub to a final polish with whiting. An 
old soft tooth brush is excellent for getting into corners, or a 
piece of flannel mounted upon a smooth stick. 

Silver plating can be done very nicely without the use of a 
battery. A simple immersion of the article to be plated in the 
proper bath will give an excellent deposit. A solution for this 
purpose will now be described. The solution is especially ap- 
plicable to such articles as watch chains, teaspoons, brooches 
and other small articles of jewelry. 

Procure four ounces of chloride of silver, twelve ounces of 
common washing soda, and five ounces of common salt. Mix 
these together with warm water so as to form a paste about 
as thick as heavy cream. The mixture is applied to the surface 
of the article to be plated by rubbing it upon the article by- 
means of a piece of cork, or a piece of flannel tied upon a- 



n6 EASY ELECTRICAL EXPERIMENTS. 

stick. All parts should be uniformly silvered. Of course the 
article must be cleaned and washed as explained in the first 
paper, and the paste is applied while the article is wet. Soft 
tooth brushes are useful in this work also. The work when 
done should be dried by rolling in sawdust and wiped dry. 

In replating old articles which have already been plated, care 
must be taken in the preliminary polishing and cleaning, to 
see that all rough edges are smoothed down. Ordinary hand 
scrub brushes, Fig. 3, are not at all bad for rough cleaning, and 
a bristle brush with crocus powder, or dry rouge, will do for 
the final polish. 

For extensive work, a small dynamo built for electroplating 
is necessary. For copper plating an electro motive force of two 
or three volts is sufficient, with moderate current. Nickel plat- 
ing requires from four to six volts, and a much stronger current. 



EASY ELECTRICAL EXPERIMENTS. 117 

CHAPTER XXXV. 



THE CONSTRUCTION AND USE OF A SIMPLE VOLTMETER. 



In the preceding chapter three electrical units were explained. 
One of these, the volt, is the standard by which we measure 
electrical pressures. An instrument designed to measure elec- 
tromotive force (electrical pressure) is called a voltmeter. There 
are several ways of constructing such an instrument, but nearly 
all depend for their action upon the mutual effects produced 
between a magnetic needle and' a coil of insulated wire carrying 
a current. The instrument now to be studied is a simple one^ 
yet it is one which may be easily constructed by an amateur 
with profit to himself in the knowledge thereby gained. 

A base board should first be secured 5 inches long, 2^ inches 
wide and Y / 2 inch thick. In its center cut a slot Y% inches wide 
and i]/ 2 inches long, with the slot running lengthwise of the 
board. At each side of the slot glue two blocks, each i T / 2 inches 
long, l / 2 inch high and % inch in thickness, the blocks being 
even with the sides of the slot. Around these, as a support, is 
to be wound in a horizontal coil 225 ft. of No. 32 double silk- 
covered magnet wire. The length and size of this wire are 
both very important. 

A magnetic needle is next to be made, whose position is to 
be inside of the coil. The best material of which to make this 
needle is a piece of watch spring, such as may be obtained for 
the "asking at an obliging watch repairer's shop. Select a piece 
\Y% inches long and % inch wide. Straighten it by bending it 
with the fingers. Heat the center of it in a small alcohol flame, 
taking care to keep the ends cool by holding wet cloths upon 
them. Then bore a small hole through the center big enough 
to allow an ordinary sewing needle to pass through. This 
sewing needle should be y 2 inch long and with very sharp points 
at each end. It may be made by breaking off an ordinary 



n8 



EASY ELECTRICAL EXPERIMENTS. 



needle until it is of the proper length, and then grinding the 
ends to a sharp point. Insert the needle through the hole in 
the piece of watch spring, and fasten the latter in the center of 1 
the needle by two small pieces of wood, circular in shape, which 
slip tightly on to the needle, and clamp the piece of watch spring 
tightly. A little glue will help make everything firm. Then 
magnetize the piece of watch spring by rubbing it with a strong 
magnet If the spring has not been softened at the ends it will 
keep its magnetism to a large degree. 




To the magnetic needle thus mounted a pointer 3 inches 
long is to be attached at right angles to the needle. The 
best material of which to make this pointer is a firm, hard 
Straw taken from an ordinary broom. Straighten it by rub- 
bing between the fingers, bore a very small hole in one of the 
wooden clamps which hold the piece of watch spring to the 
piece of needle, insert the pointer in this hole, and fasten with 
a bit of glue. The pointer should be straight, and should be at 



EASY ELECTRICAL EXPERIMENTS. ng 

right angles to the piece of watch spring. Take a small brass 
screw and screw it into one of the pieces of wood which hold 
the watch spring in place, in such a position that the pointer, 
magnetic needle and screw (counterweight) will have the re- 
lation shown in the figure. The purpose of this screw is to 
bring the pivoted needle and its pointer back to a certain position 
whenever the pointer is moved. 

To mount the needle take two pieces of thin sheet brass, each 
I inch long and T / 2 inch wide. In the middle of each and j£ 
inch from each end make a deep dent by means of a pointed 
nail and a hammer, but be careful not to punch a hole complete- 
ly through the metal. Bend each strip over at right angles in 
the middle. These straps can now be slipped down in the 
slot in the middle of the coil first made, and by a little patience 
the piece of sharp pointed sewing needle, with its pointer, 
magnetic needle and counterweight will just slip down into the 
dents punched in the sheet iron and swing freely there. It may 
be necessary to do a little filing and bending, but the needle 
and its supports can finally be adjusted so that it swings very 
freely and easily in its place. The counterweight (screw) 
should be heavy enough and in the right position to bring the 
pointer into the position shown in the figure. 

At the back of the board fasten an upright piece of thin 
wood, of the shape shown, and 4 inches wide at the top. To 
this, at the proper height, attach a piece of thick cardboard, cir- 
cular in shape. It should be supported by blocks in such a posi- 
tion that the pointer will move close to it, but not touching it. 

Be sure that the parts of the moving system have the relation 
shown in the figure, and that the needle swings very freely. 

Our instrument is now complete, except for the matter of 
marking the scale. We shall have to leave this until a later 
chapter, however, when, in addition to completing our instru- 
ment, we shall learn something regarding its use, 



120 EASY ELECTRICAL EXPERIMENTS. 

CHAPTER XXXVI. 



ADJUSTMENT AND USE OF A SIMPLE VOLMETER. 



The voltmeter whose construction was explained in the pre- 
vious chapter is not ready for use until it has been calibrated. By 
calibration we mean the fixing of points upon the scale, so that 
we can tell instantly the value of the voltage which causes a 
particular deflection. To do this there will be required a bat- 
tery of special form. The cells composing this battery can be 
; made in a very temporary and easy manner, and will answer the 
purpose perfectly. They are made as follows: 

Procure five ordinary tumblers and in the bottom of each 
place a strip of copper one inch wide and three inches long with 
a copper wire attached to it, projecting from the cell. In the 
top of each tumbler hang a strip of zinc a little longer than 
the copper strip, supporting it in the manner indicated in the 
figure below. Connections should be made to the strip, out- 
ride the tumbler, by a piece of wire firmly twisted around it. 
Place in the bottom of each tumbler a handful of blue vitriol 
(copper sulphate) and fill them with water so as to cover the 
zinc strip. Connect the zinc and copper terminals of each cell 
by a short piece of wire, and let them remain this way for 
twelve hours, at the end of which time the connecting wires 
should be removed. Then join the cells in* series — that is, con- 
nect the zinc of the first cell with the copper of the second and 
so on through the series. Be sure that the wire leading from 
*each copper strip does not touch the zinc in the same cell. The 
electromotive forces of the cells are then added together. Con- 
nect the terminals of the battery, that is, the copper of the first 
cell and the zinc of the fifth cell, if they are joined as above 
described, to the terminals of the voltmeter. The needle of the 
latter should move part way across the scale. If it does not 
reverse the connections of the wires leading to the instrument 



EASY ELECTRICAL EXPERIMENTS. 



i2r 



Now adjust the counterweight by making it heavier or lighter, 
as the case may require, until the pointer stands exactly at the 
middle of the scale. Make a line here and mark it 5 volts. Dis- 
connect one cell, leaving only four in series, and again mark the 
position of the pointer. This will give very nearly the position 
corresponding to 4 volts. Again disconnect one cell, leaving 
only three in series, and noting the position, mark it 3, Proceed 




COPPER 

Simple Voltmeter. 



thus until five points are marked upon the scale corresponding 
to 1, 2, 3, 4 and 5 volts. It will be found that the spaces between 
the various points are not quite equal, that at the center being 
the longest. On the other side of the middle point the spaces 
should be marked like those already found, with the longest 
space at the center, gradually decreasing in width until the tenth 



122 EASY ELECTRICAL EXPERIMENTS. 

line is drawn. These lines should then be plainly numbered 
from i to 10, as in the figure. 

The reasons for the process just gone through are not diffi- 
cult to understand. Each cell constructed as described gives on 
open circuit an e. m. f. 1.08 volts. The five cells in series would 
give us five times this amount or 5.4 volts, on open circuit. But 
as soon as they are attached to the voltmeter their voltage falls, 
due to the current through themselves, so that their combined 
voltage is then very close to five volts. Similarly, four cells 
give us very nearly four volts and so on. Beyond the middle 
point of the scale the points would be found to be similar in 
their position to the first five found, so we can mark their posi- 
tion without the necessity of actually constructing the cells nec- 
essary to cause the corresponding deflections. It must not be 
understood that the cells described are suitable for practical 
work. They will probably give out entirely after a few days, 
but for the purpose of adjusting the voltmeter they will answer 
as well as an expensive battery. 

A voltmeter is always connected directly to the points between 
which it is desired to measure the difference of potential. This 
is done without disturbing the connections of the rest of the 
circuit. Thus, when, we wish to measure the difference of poten- 
tial across the terminals of a motor, the terminals of the volt- 
meter are connected to these points, without disturbing the rest 
of the circuit. The instrument and the motor are then connected 
in parallel, or in shunt, these two terms being used to designate 
the same thing. 



EASY ELECTRICAL EXPERIMENTS. 123 

CHAPTER XXXVII. 



HOW TO MAKE A STORAGE BATTERY. 



A storage cell consists of a positive plate and a negative plate, 
both made of lead, and dipping into a dilute solution of sulphuric 
acid. For large cells there are always a large number of posi- 
tive and negative plates, all the positives being connected to one 
common terminal and all the negative plates to the other ter- 
minal. The storage cell described below is one that is suitable 
for the amateur's use, and is the proper size to be readily 
charged by a few gravity cells. 

Procure a piece of lead pipe 1^4 inches in external diameter, 
and 5 inches long. Having squared off both ends, solder to one 
end a circular piece of sheet lead so as to form a lead cup of the 
size just mentioned. This cup is to hold a solution of sulphuric 
acid, and must, therefore, be free from all leaks. Procure an- 
other piece of lead pipe, of the same length as before but 34 
inches in external diameter. With a ^-inch drill, bore this as 
full of holes as is possible, except for a distance of one inch 
from each end. Hammer the lower end of this tube together 
as shown at B in the figure. It need not be water tight at this 
point, but only sufficiently tight to hold a paste which will be 
described later. 

The tube B is to form the positive plate of one cell. The nega" 
tive plate is the lead cup first mentioned. To support the posi- 
tive plate so that it will not touch the negative, make a wooden 
cover for the cell of the same external diameter as the outer 
tube and % inch thick. Cut away its lower portion, so that it 
will fit snugly into the outer tube. Through its center bore a 
hole J4 inches in diameter, so that the smaller lead tube will 
just fit into it snugly. Solder to the upper end of this tube two 
lead strips, one of which is one inch long, the other three inches 
long. If these are bent over at right angles and screwed to the 
top of the wooden block after the smaller tube is in place, then 



124 EASY ELECTRICAL EXPERIMENTS, 

-t- 




EASY ELECTRICAL EXPERIMENTS. 125 

the latter will be held firmly in the block. Now immerse the 
wooden block after the smaller tube is in place, in smoking* 
hot paraffine wax, leaving it there until the wood has become 
thoroughly saturated with the hot wax. This is to protect the 
wood from the action of the acid. Do not get any wax on the 
lower part of the lead tube. 

Make a paste for the positive plate as follows. In an old 
tumbler make a weak solution of sulphuric acid, by pouring 
the latter slowly into a half tumblerful of water. Be very- 
careful in handling this acid as it destroys everything it touches, 
including the skin of the hands. Never pour water into the 
acid, but pour the acid into the water slowly as directed. Pro- 
cure at a paint shop a pound of red lead, and mix a sufficient 
amount with the half tumblerful of diluted acid to form a very- 
stiff dry paste. Stir the mixture with a stick. Then ram the 
paste into the inside of the smaller tube until the later is nearly 
filled with a solid mass of paste. Scrap off any paste that may 
have oozed through the holes and! set the tube aside to dry. 
Meanwhile solder a lead strip to the outside of the large tube, 
at the top, to serve as a connector. 

Fill the large tube two-thirds full of a solution of sulphuric 
acid, made by pouring acid into water, until there is 1-12 as 
much acid as water. A glass graduate such as amateur photog- 
raphers often use for measuring chemicals is of great assist- 
ance in this case. Then insert the wooden stopper with its at- 
tached tube into the larger tube. Our cell is now complete, 
except that a wooden box ought to be made in which to set the 
cell, to prevent its being overturned. This box can be made 
square in shape with inside dimensions a little larger than the 
cell. The latter may be set into the box, and held firmly there 
by filling all waste space with sawdust. 

To charge this storage cell three "gravity" or "crow-foot"" 
batteries will be required. These had better be purchased at 
an electrical supply store, and it is probable that most amateurs 
have them already. Join them in series, that is, join the zinc 



126 EASY ELECTRICAL EXPERIMENTS. 

of one cell to the copper of the next, and so on. To charge the 
cell, connect the terminal marked positive in the figure to the cop- 
per pole of the three gravity batteries, and connect the nega- 
tive terminal of the storage cell to the zinc pole of the battery. 

The first time this storage cell is charged, the connections 
should be left undisturbed as above for one week. At the end 
of this time it will be found to have acquired quite a charge. 
After the first charge, it is not necessary to charge it so mucn, 
10 to 12 hours being sufficient. 



EASY ELECTRICAL EXPERIMENTS, 127 

CHAPTER XXXVIII. 



HOW TO MAKE A SIMPLE TELEPHONE. 



A telephone is a source of never failing pleasure to one fond 
of experimenting. Oftentimes, too, a telephone is of great con- 
venience in affording easy communication between two widely 
separated points. The instrument is excedingly sensitive, even 
when rudely constructed, and so simple that nearly every boy 
should be able to make one. 

There are three things that must enter into the construction 
of a telephone. These are (1) a permanent steel magnet; (2) a 
coil or coils wound upon the poles of the magnet, and (3) a 
diaphragm of very thin soft iron held firmly by the edges so as 
to vibrate back and forth very close to the poles. These three 
things are shown in the sketch below, when H is the magnet, in 
this case of the horseshoe form, and C represents the coils wound 
upon two iron screws as cores, and D is a circular diaphragm 
of soft iron. To the above mentioned parts, essential to any tele- 
phone, we might add a fourth, namely, a mouthpiece shown at 
M, whose purpose is to concentrate any sounds uttered near the 
telephone upon the diaphragm. 

In the construction of such a telephone, first make a shallow 
wooden box, 4%. inches in length, 2% inches in width and 1 inch 
deep, all measurements taken inside the box. The bottom of the 
box should be of %-inch whitewood, the sides of ^-inch wood. 
Fasten the box tightly together with glue and brads. Make a 
cover for the box, J4 inch thick, and at one end cut out a hole 2 
inches in diameter. This hole should be midway between the 
long edges of the cover and its outer edge should be % inch 
from one end of the cover. 

The magnet used is a 3-inch horseshoe magnet, which can 
easily be purchased at a hardware or electrical store for fifteen 
cents. It is clamped to the bottom of the box just constructed 



128 



EASY ELECTRICAL EXPERIMENTS. 



by a wooden cleat shown at K, held by a screw at its center. The 
ends of the magnet should project a little above a line drawn 
through the center of the hole in the cover. 

The two coils are wound upon cores formed from two iron 
machine screws. The- size used is what is known as No. 10, and 
they are about 3-16 inches in diameter by 1 inch in length, and 




e. 




ONE OF THE COILS 



FRONT VIEW 

MOUTHPIECE REMOVED 



VERTICAL SECTION 
THROUGH CASE 



with flat heads. They can be purchased at a hardware store. 
The screws should be covered with a layer of stout paper, glued 
on, and then two circular wooden discs are slipped on each 
screw, whose outside diameter is $i inch. They are for the 
purpose of forming heads for the coils of wire to be wound 
upon the core. They should be J^ inch thick and should fit 



EASY ELECTRICAL EXPERIMENTS. 129 

tightly upon the screw. Make a hole in a block of wood of 
such a size that the screw will fit tightly in the holes. Screw 
it into the block until it projects Y inch from the block. The 
block simply serves as a handle by which to hold the coils while 
winding and will be thrown away after it has served its pur- 
pose. Place the wooden heads in position upon the screw, and 
place them at such a distance apart that there is a clear space 
of ]/ 2 inch between them. Wind this space full of No. 36 
double silk covered magnet wire. Remove the coil from the 
block which has served for a handle, and there should now 
be a coil whose outside diameter is % inch, and whose extreme 
length is 24 inches with an iron core made of a screw which 
projects % inch from one end. Proceed in a like manner with 
the other screw, forming a second coil exactly like the first 
one. 

These coils are to be held with the projecting end of the 
cores firmly clamped against the poles of the horseshoe mag- 
net. This can easily be done by screwing the projecting ends 
into a strip of hard wood, which is 2^4 inches long, y 2 inch 
wide, and a scant y inch thick. Bore two holes in this, % inch 
apart and equally spaced each side of the center of the strip. 
These holes should be of just the right size so that the iron 
screws will fit them tightly. The screws should project a little 
through the back of the wooden strip. The strip is then screwed 
to the base wood board forming the back of the box first con- 
structed, in such a manner that the screws are each held firmly 
against the poles of the magnet. Connect one end of one coil 
to one end of the next in such a manner that if a current should 
flow through the coils it would go around one coil in a direc- 
tion opposite to that in which it goes around the other. Con- 
nect the free ends to the binding posts shown. 

The diaphragm D is v of thin soft iron called ferrotype iron, 
such as is commonly used by photographers. It can be pur- 
chased of a photographic supply store. Cut out a circular piece 
2,y 2 inches in diameter. Clamp it to the front of the cover cov- 



130 EASY ELECTRICAL EXPERIMENTS. 

ering the hole cut in the latter. It is held firmly all around! 
its ^dges by a circular block of Wood S, but this block must 
not touch the disc except at its edges. Hence it is cut away 
on the under side as shown. The diaphragm should be free to 
vibrate at its center, and so it must not touch the ends of the 
iron screws around which the coils are wound, although it 
should be as close as possible to them. 

The mouth piece M is made of heavy cardboard. The stiff 
cover of a blank book is excellent material. It should be 2 
inches in diameter at the large end, and Y% inches in diameter 
at the small end. The cover of the box is fastened on by means 
of small brass screws. 



EASY ELECTRICAL EXPERIMENTS. 132 

CHAPTER XXXIX. 



THE DESIGN OF A SMALL DYNAMO. 



PART I. 



One of the most common problems that the amateur meets 
is the problem of the proper design of small dynamos and mo- 
tors. In the following chapter an attempt will be made to explain 
the methods and principles involved, and the various steps in 
the calculation will be gone over. It will be assumed, however,, 

that the reader has a fair 
know ledge of electrical 
terms, and a familiarity 
with the essential parts of 
a dynamo or motor. 

First of all we must as- 
sume that we are to build 
a machine that will give us, 
when run as a dynamo, a 
certain output in watts. The 
machine to be described 
will have a maximum output of 75 watts at a pressure of 50- 
volts. We are obliged to rely for our starting point upon the 
experience gained by others. It has been found that for this 
type of machine a speed of 2400 revolutions per minute is a 
good value to use; also that a velocity of the conductors upon 
the armature of 30 ft. per second is about the highest we can 
go with safety. Knowing these two things, it is easy to cal- 
culate the size of our armature. If we multiply the speed at 
which the conductors move (30), by 12, and divide the product 
by 3.14 and again by the number of revolutions per second (40), 
the result will be the diameter sought. In this case the product 
of 30 and 12 is 360. Dividing this by 3.14 gives 114.6. Divid- 
ing again by 40 gives 2.865 a s the diameter of the armature 
we are to use. This is very nearly the same as 2^ inches, and 




132 EASY ELECTRICAL EXPERIMENTS. 

is the average diameter of the armature, measured to the center 
of the conductors. The outside of the armature should be a 
little larger than this. To use even figures, let us assume the 
outside diameter of our armature to be 3 inches. 

In the design of armatures for large machines, a less num- 
ber of revolutions per minute must be chosen. A machine of 
y 2 horse power (373 watts) should have a speed of about 2200 
revolutions per minute. A one-horse power dynamo should run 
at about 2000 revolutions per minute, and a two-horse power 
dynamo is usually run at about 1800 revolutions per minute. 

The armature which we will use will be of the toothed type, 
shown in Fig. 1. The actual number of slots used is immaterial, 
if it is only an even multiple of the number of commutator seg- 
ments to be used. We will choose twelve slots and twelve teeth 
for our armature. The number of commutator segments varies 
with the voltage to be employed ; and also with the current gen- 
verated. Of course, the number of segments should be an even 
^number, and is almost always some multiple of 3 and 2; e. g., 
12, 18, 36, etc. 

Since ours is a low voltage machine a very few segments 
will suffice, as far as insulation goes. But it must be remem- 
bered that the greater the number of segments the smoother will 
be the current generated. On general principles, not less than 
six segments should ever be used, and for machines of no volts 
and upward, twelve or more segments should always be used. 
Because of ease of construction, we will choose six commuta- 
tor segments for our machine. The above remarks apply to 
machines with one pair of field poles. Machines with two pair 
(4 poles) will require double the number mentioned. 

The conductors wound upon the armature will lie closely 
packed in the slots. Imagine that we have built our armature, 
and could cut it open directly across the conductors. How 
many conductors could we count? This is the next question 
we shall answer. 

Their number depends upon their size, of course, and their 
:.size depends upon the current they are to carry. 



EASY ELECTRICAL EXPERIMENTS. 133 

Now if the output of our dynamo is to be 75 watts at 50 
volts, the current generated must be 1^ amperes. Usually we 
have to allow also for the current which supplies the field 
coils, assuming the latter to be in shunt with the armature. 
In this case we will assume that the field current has a value of 
y 2 amperes. It is usual to allow in small machines an area of 
400 circular mils per ampere, in determining the size of wire 
£n the armature. On larger machines (1 to 2 kilowatts), at 
least 600 circular mils per ampere should be allowed. Our ma- 
chine will have a drum armature and will therefore have two 
parallel circuits through the armature. So that each conductor 
carries one-half the above current, or one ampere. Therefore 
the conductors on our armature must have an area of 400 cir- 
cular mils. This means that we must use No. 24 magnet wire 
upon the armature. This, when insulated with double cotton 
covering, has an outer diameter of .03 inches. 

The width of our slots if they are to take up one-half of the 
circumference of the armature is }i inch, and if they are 5-16 
inch deep, it will give us a well proportioned tooth. Assuming 
these dimensions, we can have eight layers of wire in each slot. 
This allows 1-32 inch for insulation at the bottom of the slot, 
and 1-16 inch clearance at the outside, which will be necessary 
for binding wires. Assuming the same thickness of insulation 
on the sides, we can get 11 turns in each layer. So the number 
of conductors in each slot is the product of 11 and 8, or 88; 
and the total number of conductors in all slots is 88 times 12, 
or 1056. 

We will continue the design of our machine in a following 
chapter. 



134 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XL. 



THE DESIGN OF A SMALL DYNAMO. 



PART II. 



Having calculated the number and arrangement of conductors 
upon the armature, as described in the preceding chapter, we 
will next take up the necessary calculations for the field magnet. 
We will assume that it is to be of the bi-polar form, of the gen- 
eral shape shown in the accompanying figure. First, as to di- 
ameter of armature space. The outer diameter of armature is 
three inches. Allowing 1-32 inch clearance, the diameter of the 

armature space should 
be 3-16 inches. Next, 
how large should the 
core of the field magnet 
be? This will depend 
upon the strength of 
magnetic field that we 
are to force through it. 
There is a definite re- 
lation between the 
strength of magnetic 
field, the speed, the elec- 
tromotive force and the 
conductors on the arma- 
ture. In every dynamo, 
the product of the num- 
ber of conductors on 
the armature, multiplied by the strength of field, is equal to the 
electro-motive force in volts multiplied by 100,000,000 divid- 
ed by the number of revolutions per second. 
In one machine, the voltage at full load is to be 50. But 




EASY ELECTRICAL EXPERIMENTS. 135 

allowing for an inevitable loss in the armature, we will assume 
voltage to be 55. This means a loss of 10 per cent, which is 
none too much for a small machine. Applying the rule just 
given, we multiply this by 100,000,000 and divide by 40 (the 
revolutions per second), getting as an answer 137,500,000. This 
represents the product of the number of conductors on armature 
by the strength of field. But we have already calculated the 
number of conductors (1,056). Consequently we have but to 
divide 137,500,000 by 1,056, giving us 130,200, the strength of 
field necessary to give us 55 volts at a speed of 40 revolutions 
per second. 

Now how large shall be our field magnets? That depends on 
their material. If they were of cast iron they will be quite 
large. If we make them of cast steel, they will be much smaller. 
Consequently, we will make them of soft cast steel. This ma- 
terial will carry easily 88,000 lines of magnetic force for every 
square inch of cross section. 

Since there will be a large amount of leakage of magnetism 
in so small a machine, the 130,200 lines of force will have to 
be increased considerably. Multiplying this by 1.2 gives us 
156,240 as the number of magnetic lines to be sent through 
the field magnet. 

Dividing this by 88,000 gives 1.77 square inches as the area 
of one field magnet core. Further calculation shows that the 
diameter must be 1.5 inches to give us this area. These dimen- 
sions are shown in the figure. 

The next important dimension of the field magnet is its length 
parallel to the shaft of the armature. This length is determined 
solely by the allowable density of magnetism in the air gaps 
between armature and field. The magnetism has to cross a gap 
of 1-32 inch on each side of the armature. If we make the 
field magnet poles too short, the density in this gap will be 
too great. If we make them too long, we shall waste material. 
Their proper length is determined by allowing one square inch 
for each 20,000 lines of magnetic force that cross the air gap. 



136 EASY ELECTRICAL EXPERIMENTS. 

So our air gap will have an area of 6.51 square inches, obtained 
by dividing 130,200 by 20,000. If we should take a string and 
measure the length of arc on field magnet, we should find it 
to be zVz inches. Measuring the same arc on surface of arma- 
ture, its length is z z A inches. But since only half the surface 
of the armature is iron, the effective length of arc on armature 
is 1 23-32 inches. Taking the average of 1 23-32 with 2>H> gives 
2 18-32 inches as the effective length of arc across which the 
magnetism must cross. Knowing this length, and knowing that 
the area of air gap measured parallel to shaft must be 6.51 
square inches ; dividing the latter by the former, gives us a 
length a little in excess of 2^/2 inches. In order to make dimen- 
sions an even number, will call the length of pole piece par- 
allel to shaft 2j4 inches exactly. 

Our next chapter will be taken up with a calculation of field 
winding, and a consideration of practical details. The theoreti- 
cal work thus far is simply to fix dimensions and shape, and 
the practical side will now be emphasized. The dimension given 
in the figure as 3 11-16, was derived from a consideration of 
diameter of armature and of clearance necessary to top and 
bottom of armature. At the bottom are two projecting lugs }i 
inch square for fastening field frame to base. The casting 
shown in figure is in one solid piece. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XLI. 



137 



THE DESIGN OF A SMALL DYNAMO. 



PART III. 



Final calculations must now be made to determine the size 
and amount of wire upon the field coils. The latter have to 
furnish enough magnetic force to send 156,240 magnetic lines- 
through the iron frame, across the air gap and through the 
armature. Let us begin with the air gap between armature 

and field. It is 1-32 inch 
wide on each side of the 
armature. That is, the 
magnetism has to cross a 
layer of air equivalent to 
1-16 inch thick. To cal- 
culate the ampere turns 
required for this, multi- 
ply the density of mag- 
netism in the air gap 
(20,000) by the width of 
gap (1-16 inch) and by 
.313. This gives as a re- 
sult 391. Next find how 
many ampere turns will 
be required for the field 
magnet. The total length 
of steel traversed, be- 
ginning at A and extend- 
ing around to B is about 
11 inches. Multiply this 
by the density (88,000) and by .313. This gives us 240,384. 
This would be the amphere turns required if steel were no 
better a conductor of magnetism than air. But as a matter 




138 EASY ELECTRICAL EXPERIMENTS. 

of fact soft steel, under the above conditions, has a conduc- 
tivity 800 times greater than air. So we will only need one 
eight-hundredth as many ampere turns as above calculated. 
This gives us 300 as the ampere turns required for field. For 
the armature teeth, which are 5-16 inch deep and of an aver- 
age width of 5-16 inches, there will be needed 26 ampere- 
turns. And for the body of the armature core there will be 
needed 75 ampere turns. Adding these all together gives a 
total of 792 ampere turns. To this we will add 25 per cent, 
to make up for armature re-actions, giving a total of 
990. Let it be decided that our field current should 
be H ampere. So we will need 1,980 turns of wire 
on our field magnet. We find the size of wire to be used 
in just the same way that we found the size in the armature 
—namely, by allowing 400 circular mils per ampere. This 
shows us that No. 27 magnet wire must be used. Calculat- 
ing the length of 1,980 turns of No. 27, we find that it would 
take about 990 feet, and have a resistance of about 60 ohms 
when hot. Now this would give us a current of 1 1-5 am- 
peres, which is too much. Our assumption of % ampere then 
was too high, and we cannot use No. 27 wire. Let us assume 
a field current of % ampere. This would require 3,960 turns 
of No. 30 magnet wire, whose total length would be 1,980 feet, 
with a hot resistance of 210 ohms. This gives us the right 
value of current, assuming an e. m. f. of 52% volts. The wire 
will be wound on the core in 14 layers on each spool of 
approximately 135 turns each. 

The weight of wire required is about one pound. 

The accompanying figure shows the finished field magnet 
with windings in place. The cores are first wound with sev- 
eral layers of heavy paper glued in place. Then four heavy 
split washers of cardboard or fuller board are slipped on the 
core, protecting the ends of the coils from contact with the 
iron. The wire should be wound evenly, and the two coils 
connected in the usual manner. 



EASY ELECTRICAL EXPERIMENTS. 139 

Castings similar to the above may be bought of dealers in 
electrical supplies, or may be made from patterns. If made 
of cast iron, however, the cross section will have to be dou- 
bled, and the field windings recalculated. 

The armature of our dynamo is to be made up of a large 
number of discs, cut from thin sheet iron. These may also 
be bought of the form and dimensions given in a previous 
chapter. About 60 of them make a pile one inch high, so that 
150 discs will be required. 

Directions will be given in the following chapter for wind- 
ing the armature, building commutator, and finishing up the 
machine. 



140 EASY ELECTRICAL EXPERIMENTS. 

CHAPTER XLII. 



THE DESIGN OF A SMALL DYNAMO. 



PART IV. 



The armature of our dynamo is to be of the well known 
drum type. The armature core, the shape of which was 
shown in Chap. 1, is made up of a large number of toothed 
discs punched from thin sheet iron. These discs may be 
bought of the dimensions given, at various electrical sup- 




ply houses. About sixty of them are needed to make a pile 
one inch high, so we will need 150 such discs. They are 
mounted upon a shaft of soft steel, which is 5-16 inch in 
diameter at the ends and % inch in diameter in the middle, 
and should be at least 9% inches long. The central portion 
is threaded as shown in Fig. 1, and two nuts, clamping 
against two stiff washers, bind the whole very tightly to- 
gether. The discs must be held very firmly and cannot be 
clamped too tightly. When threading them on cut the ends 



EASY ELECTRICAL EXPERIMENTS. 14s 

of the teeth of those discs which occupy a position % inch 
each side of the center, so that they are 1-16 inch shorter 
than the teeth in remaining discs. This makes a slot which 
will be filled with binding wires as explained later. 

Having mounted the core upon the shaft, in the position 
indicated by the dimension lines in Fig. 2, it must next be 
carefully covered with an insulating covering to keep all 
wires from contact with the iron. First go over every cor- 
ner and sharp bend in the slots and on end nuts, covering 
these places with a layer of thin cotton cloth, fastened in 
place with shellac. Then apply a layer of the cloth to the 
sides and bottoms of the slots, the ends of armature, and 
other places where the wire is especially liable to touch the 
iron, using shellac as a glue. Wrap two or three layers of 
cloth around the shaft, for a distance of two inches from 
the ends of core. 

In winding the coils in place proceed as indicated in Fig. 
1. There are twelve slots on armature, and we are to have 
only six coils. So each coil will occupy two slots. This is 
an advantage, as it lets the wires clear the shaft with little 
difficulty. Begin at slot number one, and wind in eight lay- 
ers, carrying the wire around the armature across the end 
at the back, and returning through slot number six. There 
should be eleven turns in each layer, using number 24 double 
cotton covered magnet wire. This completes coil number 1, 
and the wire may be cut off leaving a projecting end six 
inches long. Its beginning should be tagged with a small 
tin tag marked B-l, and its end tagged 3 E-l, and the two 
ends twisted together temporarily. 

Coil number 2 begins in slot number 3, and occupies slots 
3 and 8. Its ends should be tagged B-2 and E-2, and twisted 
together. Coil number 3 occupies slots 5 and 10. Each coil is 
put on in this manner, skipping one slot between each coil. 
Of course they all overlap on the ends, but this can be made 
to present a neat appearance, if pains be taken. 

When all are in place, stout brass binding wires are 



142 



EASY ELECTRICAL EXPERIMENTS. 



wound tightly in the slot left vacant at center of core, and 
soldered in place. These keep the copper wires from flying 
out when armature rotates rapidly, and are absolutely nec- 
essary. About one pound of magnet wire is required for 
armature. The whole armature should now be given a coat 
of shellac, and then placed in a warm oven to thoroughly 
dry. 

A six section commutator is easily made by mounting a 
piece of brass tubing 1% inches in external diameter and 
1% inches long upon a wooden hub which may be driven 
tightly upon the shaft. Before doing this, divide the sur- 
face of the brass tube into six sections by lines parallel to 
its axis. In the center of these sections and at either end, 
bore two holes through which pass two 3-8 inch brass 
screws. Then with a hack saw cut the tube into six por- 




tions, sawing along the lines first drawn. The screws al- 
ready inserted hold sections in place. After sawing remove 
each section and file off all sharp edges. If a lathe is avail- 
able, the surface of commutator should be turned down 
smooth and circular, after sections are again in place. 

Connect the end of coil number 1 (E-l) and beginning of 
coil number 2 (B-2) to a section of commutator. Connect 
E-2 and B-3 to next section, E-3 and B-4 to the next, and so 
on around the armature. These connections should be made 
smoothly and uniformly. It is best to make connections 
by soldering, as this throws less strain upon the screws in 
commutator. A little copper ear may be clamped under each 
screw to which connections may be soldered. 



EASY ELECTRICAL EXPERIMENTS. 143 

CHAPTER XLIII. 



THE DESIGN OF A SMALL DYNAMO. 



PART V. 



Having made the armature and field magnets as previously 
described, the next thing to be done is to provide suitable 
means for mounting them in proper relation to each other. 
For this purpose a bed plate must be provided of a shape 
shown in Fig. 3. The general dimensions are there given, 
although details regarding the machine are left for the 
amateur to work out for himself. The bed plate should be 
of brass. It cannot be made of iron, for the ends of the 
field magnets are to rest upon it, and if made of iron much 
of the magnetism would pass through the iron base, in- 
stead of through the armature. In the center are two holes, 
% inch square, which are to receive the projecting lugs on 
the polar ends of the field magnets. (See Chap. II.) The 
amateur will have to see that the dimensions on field mag- 
net and on base, are so adjusted that the former will fit the 
latter. The base should be about 1 inch high. The project- 
ing lugs slip down into the holes provided, and bolts screw- 
ing up into the lugs, provided with large washers, clamp the 
base and field magnet frame firmly together. 

Next, bearings must be provided for. They should be 
made of brass castings also. The two bearings are not alike, 
for one of them must be made so as to serve as a support 
for brushes, while the other one is a plain simple bearing. 

The former is shown in plan in Fig. I, and in elevation 
In Fig. 2. 

Measure the height of the center of the circular armature 
space above the top of the base. This is the height of the 
center of the shaft, and is therefore the height of the center 
of bearing above base. In making patterns for these bear- 



H4 



EASY ELECTRICAL EXPERIMENTS. 



J 



^ 



frfa 



3® 

gar 



Fig. I 




i^C 




ings, allowance should be made for loss of metal in finish- 
ing, which will amount to at least 1-16 inch. 

The brush holder shown in Fig. 2 is very simple, and fairly 



EASY ELECTRICAL EXPERIMENTS. 



145 



efficient. Each brush holder consists of a brass spring S, 
a brass ferrule A, and a carbon rod C. The ferrule A is 
provided with a shoulder as shown, and a hole is drilled 
through the spring to receive the smaller part of the ferrule. 
The latter and the spring are then soldered together. The 
carbon rod C should be about 3-16 inch in diameter, and 
should fit the hole in ferrule snugly. A screw passing 
through the side of ferrule clamps carbon rod firmly. The 
springs are so adjusted that the carbon rods are pressed 
firmly against the top and bottom of commutator. They 
should slant a very little to the back, imagining the eye 




-r- 



□ 



<h -* 



Sir 



F.&. 3 

to be looking in direction that commutator is to revolve. 
The springs should be about 3% inches long, 1-32 inch thick, 
and % inch wide. In Fig. 2 the upper holder is shown in 
section, and the lower holder in elevation. Each spring 
must be carefully insulated from the brass supporting arm. 
This is done by putting pieces of hard rubber or hard fibre 
above and below the spring and by also providing a washer 
of the same material surrounding the screw which clamps 
the springs to the support. 

The field coils, after being joined in series, are then con- 
nected directly to the brushes. The brushes also serve as 



i 4 6 EASY ELECTRICAL EXPERIMENTS. 

terminals for the machine, making the field coils to be in 
shunt with the external circuit. 

When run at 2,400 revolutions per minute, the machine 
will give 60 volts on open circuit, and will give a voltage of 
50 when delivering a current of 1% amperes. Many details 
regarding construction have been left to the amateur to 
work out, as the purpose of this series of articles has been 
to teach the main principles of dynamo design, rather than 
the mechanical details which any ingenious amateur may 
work out for himself. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XLIV. 



147 



HOW TO MAKE AN ELECTRIC GYROSCOPE. 



PART I. 



The gyroscope has long been known to physicists as an 
interesting scientific toy. In an elementary form it has been 
used probably by many of the young readers of this book. 
The form usually sold in toy shops, consists of a lead wheel 
with an extremely heavy rim mounted in a pair of pivots 
supported on a ring. When set into extremely rapid rotation 
by means of a string wound around the axis, the wheel may 
be made to perform numerous interesting feats such as hang- 




ing by one side from the edge of a table or ether convenient 
support. The common top so dear to every boy's heart is 
only a special form of gyroscope. Every one knows that as 
a top spins rapidly it will stand upon its point in apparent 
defiance of the law of gravity, and if displaced from its 
position will tend to assume an erect position again. If we 
take a bicycle wheel from its frame and grasp the support- 
ing axle in the two hands, we may tilt the wheel easily to 
any angle provided the wheel be at rest. If however, we 



148 EASY ELECTRICAL EXPERIMENTS. 

set the wheel spinning quite rapidly and then try to change 
the direction of rotation of the wheel by grasping the axle, 
we shall find that it is almost impossible to suddenly wrench 
the wheel out of its normal position. 

In all these cases, it is apparent that a body in rapid mo- 
tion possesses properties which a body at rest does not pos- 
sess. They are only specific illustration of the important law 
of motion which states that„a body once set in motion can- 
not of itself change either the direction or the value of its 
own motion. 

In the case cited the motion soon ceases and the effect is, 
therefore, only a temporary one. In the instrument to be 
described in this paper electrical means are employed to 
keep the body in constant rotation, thus making possible the 
demonstration of many interesting physical facts. One of 
these which is of especial interest is the visible demonstra- 
tion of the rotation of the earth upon which we live. We 
ordinarily accept as true that the earth rotates on its axis; 
the gyroscope makes this rotation a visible fact. 

We will need first of all, a heavy brass wheel such as is 
shown in Fig. 1. This wheel is 3 inches in external diameter 
and has a heavy rim % inch thick, the width of this rim 
being % inch. The wheel may be turned from a % inch plate 
of brass. Especial care should be taken to accurately cen- 
ter and turn the wheel. The central portion of the wheel 
should be turned down to a thickness of % inch, the rim 
being of the dimensions already given. 

On one face of the wheel and within the rim, is to be 
mounted a piece of soft iron shown at S which is 2% inches 
long, 7-16 inch wide and 1-16 inch thick. It is fastened in 
place by four flat head iron screws counter sunk flush with 
the surface. On the other side of the wheel and at right 
angles to the first piece of iron is mounted a second piece 
indicated by the dotted lines. 

Having done this, bore through the exact center of the 
wheel a hole which is a scant % inch in diameter. Through 



EASY ELECTRICAL EXPERIMENTS. 149 

this hole is to be driven very tightly a shaft whose total 
length is 2% inches, the wheel being in the exact center of 
the shaft. The shaft is turned down for *4 inch from each 
end to a diameter of % inch thus forming two shoulders to 
fit in bearings to be described later. If any doubt exists 
as to the shaft being exactly in the center of the wheel a 
test should be made at this point and the wheel turned 
down by taking a very light cut until both inside and out- 
side of rim run perfectly true. 

At C are shown two contact wheels made of 3-16 inch 
brass driven tightly upon the shaft. These contact wheels 
are so made that they will make contact with a brush which 
is to press upon them for one-eighth of a revolution, then 
break the contact during the next quarter revolution, then 
make contact during the next quarter and so on. Accordingly 
they have the shape shown in the left hand part of the 
figure, the diameter measured between circular portions be- 
ing % inch. They should be placed in the position indicated 
in the figure, the discs on opposite side of wheel being 
twisted around so as to be at right angles to each other. 
This point will be explained more fully later, after we har€ 
built the remaining parts of the machine. 



250 EASY ELECTRICAL EXPERIMENTS. 

CHAPTER XLV. 



HOW TO MAKE AN ELECTRIC GYROSCOPE. 



PART II. 



In the last chapter the rotating part of our instrument 
was described consisting of a brass wheel with an extremely 
heavy rim supported on suitable shaft. The field magnets 
and supporting frames of this motor will now be described. 

A view of the frame is given in Fig. 2 with two of the 
four coils composing it in place. It consists of two side 
strips of iron marked A and D which are 4^ inches long, % 
inch wide and % inch thick; the end pieces of the frame 
C and B being made of pieces of brass % inch square and 
2y s inches long. At a distance of 1 5-16 inches from the 
end of the iron strips, bore two holes 3-16 inch in diameter. 
These are to support the circular iron cores shown at H. 
These circular iron cores are of the dimensions given in the 
figure and are drilled and tapped at one end so as to be 
fastened to the iron strips by round headed machine screws 
passing through the holes already drilled. The frame is 
fastened together at the end by iron screws passing through 
the strips of iron and into the ends of the brass strips. 
Extreme care must be taken to see that the frame is rigid, 
and peir^ectly balanced throughout. To secure these qualities 
care should be taken to finish the various strips carefully. 
After the frame is screwed together bore with a small drill 
a hole close to the end screws and passing through the iron 
strips into the brass strips to a depth of % inch. In these 
small holes drive a tight fitting pin which will help to 
prevent racking of the frame. 

Coils are next to be wound upon the four inwardly pro- 
jecting cores. Two of these are shown in the figure, the 
other two being omitted to make the diagram clearer. 
Turn out from a piece of brass, eight pieces 1-16 inch thick, 



EASY ELECTRICAL EXPERIMENTS. 



I5i 



and 15-16 inch in diameter, with a hole in the center just 
big enough so that the disc may be driven tightly upon 



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Fig. 2 







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the circular iron cores, to form heads to contain the wire 
to be wound upon the cores. 

About four ounces of number 30 double silk covered mag- 
net wire will be required. Wind each core with a layer of 
paper, fastened on with shellac, and cover the inside of 



1S2 EASY ELECTRICAL EXPERIMENTS. 

the brass head with a paper disc, so that the wire cannot 
possibly come in contact with the core. Then wind the 
coils on the four iron cores, so as to make a coil 15-16 inch 
in diameter. Connect all the coils in series when they are 
complete, connecting them in such a manner that a north 
pole of one coil will be opposite to the south pole of the 
coil opposite. 

Before fastening the cores in place to the side strips A 
and D, bore a hole in the exact center of the two strips A 
and D, the holes being % inch in diameter. To these holes 
are to be fitted brass bushings of the shape shown at the 
left of the figure. These brass bushings are to form bear- 
ings for the support of the revolving wheel described in the 
last chapter, and accordingly must be flush with the sur- 
face of the iron on its inner face. The bushings had better 
be threaded into the iron and fastened by means of a set 
screw. 

We must provide means for supporting the apparatus when 
it is completed. It is to be supported by being hung upon 
the steel pivot P. This pivot is threaded into a brass strip 
% inch wide bent into the shape shown. In order to exactly 
balance the machine it will be necessary probably to shift 
this piece of brass a little so that the screws which fasten it 
to the frame pass through slots cut in the brass instead 
of through holes. 

We are now ready to put the apparatus together, but the 
description of this will have to be left to the following 
chapter. 



EASY ELECTRICAL EXPERIMENTS. 
CHAPTER XL VI. 



153 



HOW TO MAKE AN ELECTRIC GYROSCOPE. 



PART III. 



The rotating and the fixed parts of our instrument having 
been completed, they can be assembled together after the 



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The Electeic Gyroscope. 



154 EASY ELECTRICAL EXPERIMENTS. 

manner indicated on page 153. It will be seen that 
the wheel W is mounted so as to swing freely in the center 
of the frame already constructed. It is essential that this 
wheel should run very smoothly and evenly and should be 
perfectly balanced. The iron armatures fastened to its sides 
should pass very close to the poles of the electro magnets C 
of which there ar»e two on each side of the wheel, without 
touching the latter. For this reason the wheel can have 
hardly any side motion. The strip of brass into which the 
pivot P is fastened, must be insulated from the frame. To 
acomplish this strips of hard rubber are placed between it 
and the frame and also under the head of the screws which 
clamps it, the latter being provided as well with an insulat- 
ing bushing. 

At the bottom of the frame are attached two springs 
marked S which are also insulated from the metal frame but 
are connected with each other and to a piece of wire hang- 
ing from the bottom of the frame to a distance of about one 
inch. The four coils are connected in series in the manner 
previously described and one terminal of the wire is con- 
nected to the insulated pivot P. The other terminal of the 
coils is connected to some part of the metal frame. 

A suitable base shown in the figure is provided with an 
upright post U which carries at the upper end the heavy 
strip of brass B. The height of this post should be such as 
to allow the frame to swing clear of the base by about % 
inch, Directly under the middle of the frame a hole is to be 
bored in the base to a depth of % inch into which is to be 
poured a globule of mercury. The projecting wire already 
mentioned should dip into this mercury when the frame is 
suspended in position. The pivot P should be very sharp and 
hard and should bear upon a piece of hardened steel fast- 
ened to the brass strips B so that the gyroscope may turn 
with very little friction into any position. 

Its action is as follows: Current is led into the lower mer- 



EASY ELECTRICAL EXPERIMENTS. 155 

cury cup by a wire as indicated, thence to the insulated 
springs S, to the contact maker K to the frame of the ma- 
chine, through the coils C to the pivot P and thence out of 
the wire shown at B. The action of the contact maker K is 
as follows. When the iron strip H is % of a revolution from 
the poles of C, K should make contact with S, closing the 
electric circuit through C which causes H to be attracted. 
This should continue until H is exactly opposite to the poles, 
when the contact should be broken. Now for % of a revolu- 
tion, the circuit will be open, but after this interval the strip 
on opposite side of the wheel should be % of a revolution 
from the magnets on that side. The contact maker on that 
side should now close the circuit and act in just the manner 
that K acts when it comes in contact with S. If three or 
four strong bi-chromate cells be used the wheel ought to 
revolve at a high rate of speed. 

Its gyroscopic action, that is, its resistance to any change 
in the plane of its rotation is very marked. If no force 
were acting on the wheel it would be impossible for it when 
once started to change the plane of its rotation. If the pivot 
P be without friction the base may be turned about in any 
direction without altering the position of the wheel H. Sup- 
pose the wheel to be started so that its plane points exactly 
north and south. It will continue to run in the direction in 
which it is pointed even though the base A and the earth 
under A should change their position. Now the earth is con- 
stantly rotating and what is north for a person in one place 
is not north for a person in another place, for the reason 
that the meridians of longitude converge at the pole and are 
therefore not parallel. If the wheel be started to rotating in 
a north and south meridian at a given time, it does not mean 
that the wheel will continue on this meridian but it will al- 
ways continue to rotate towards some fixed point in space. 
After a time, therefore, the wheel will apparently have 
changed its direction of motion and will no longer point 



156 EASY ELECTRICAL EXPERIMENTS. 

north and south. It is not the wheel whi.cn has changed, 
however, but the earth. By making a small sphere and draw- 
ing lines upon it to represent the meridians, it will be very 
easy to understand this matter. Of course it is understood 
that the force of gravity will make the wheel to always 
rotate in a plane passing through the center of the earth, but 
this can in no wise affect the horizontal direction in which 
the wheel points. 



EASY ELECTRICAL EXPERIMENTS. 157 



CHAPTER XL VII. 



AN ELECTRICALLY LIGHTED LAMP. 



The electric spark is quite commonly used to ignite gas, as 
all readers are doubtless aware. For this purpose either the 
spark from the secondary of a rather powerful induction coil, 
or the direct spark caused by the breaking of an electric cir- 
cuit in proximity to the stream of gas, may be used. The 
former plan has the advantage that the apparatus may be 
worked at a distance by the mere pressing of a button, while 
in the latter case the apparatus must be worked at the place 
where the light is desired. It has the advantage, however, 
that the apparatus required is simpler and cheaper than in 
the first case. 

Not only may illuminating gas be thus ignited, but the 
vapor from highly inflammable liquids, like gasoline and 
alcohol is also easily lighted. Electric cigar lighters are made 
containing alcohol, and a wick, so arranged that the wick 
will burst into flame when a spark occurs near it. 

The small alcohol lamp described in this chapter cost but 
little to make, and illustrates the principles involved very 
clearly, and may be of some practical use as well. 

There will be needed first of all, a small wide-mouthed 
bottle, something like a horseradish bottle, but smaller. Those 
in which glue and paste are often put up are about the right 
kind. Fit to this a smooth cork. Through the center of this 
cork is to be fitted a brass" or iron tube, long enough to pro- 
ject Y2 inch above and below the cork, and about % inch in 
diameter. The brass tubes of which curtain fixtures are often 
made will answer the purpose. At the bottom the tube is 
cut square across, but at the top a lip is left projecting, as 
shown at C in the accompanying figure. Through the tube is 
to be thrust a circular wick such as are commonly used in 
torches. 

At H is shown a wooden handle into which is fastened a 
metal rod, about 3-16 inch in diameter. An old button hook 
with the end cut off will answer very nicely. On the end of 
this rod is slipped a rather stiff metal spring, shown at B, 



158 



EASY ELECTRICAL EXPERIMENTS. 



with one end straightened, and projecting about y 2 inch. The 
other end is coiled about the rod and is soldered to the latter 
at A. 

At K is represented an ordinary spark coil, such as may be 
bought at dealer in electrical supplies. It can be made very 
easily however by an ingenious boy. Make a bundle of soft 
iron wires, the bundle to be about 12 inches long and % inch 
in diameter. The wires themselves should be not larger than 
No. 20, and should be very straight and uniform in length, so 

C 




Lights a Lamp, 

as to form a very compact bundle. On this as a core, and 
carefully insulated therefrom, wind six layers of No. 14 double 
cotton covered magnet wire. The coil thus made is represe- 
sented merely at K. 

Now connect one terminal of the coil to one terminal of a 
battery of three sal-ammoniac cells, the othei terminal being 
connected to the brass tube at T. The remaining terminal of 
the coil is connected to the metal rod at A. 

Now if the handle H be held in the hand, and the spring B 



EASY ELECTRICAL EXPERIMENTS. 159 

is drawn firmly across the projecting lip at C, a heavy spark 
will be produced very close to the end of the wick. If the 
wick be saturated with alcohol this spark will be sufficiently 
heavy to ignite the alcohol. The bottle should be kept well 
filled. 

In order to keep the wick moist, and to prevent waste of the 
alcohol, a small brass cap should be provided which fits tightly 
over the end of the tube when the apparatus is not in use. 



i6o EASY ELECTRICAL EXPERIMENTS. 



CHAPTER XLVIII. 



A SIMPLE ARC LAMP. 



There are two kinds of electric lamps— incandescent lamps 
and arc lamps. The former are operated by sending a cur- 
rent of electricity through a very small thread of carbon con- 
tained in a glass bulb from which the air has been ex- 
hausted. The passage of the current through the carbon 
thread heats it very hot, so that it is capable of giving out 
light. 

Arc lamps are operated by causing a current to pass be- 
tween the tips of two carbon sticks, which are separated 
by a short space, usually about one-half inch in length. 
Ordinarily it is impossible to make an electric current pass 
from one body to another, unless the pressure be very great. 
But if two sticks of carbon connected to an electric circuit 
of proper strength be touched together and then separated 
by a short distance the space between them becomes filled 
with the vapor of carbon, through which the current will 
pass, at the same time heating the tips of the carbons to an 
intense white heat, which gives off a dazzling light. 

As the carbons burn away it is ordinarily necessary to 
provide means for feeding them toward each other as fast 
as they are burned. This calls for a rather complicated ar- 
rangement of magnets and other devices. The amateur can 
construct a very simple arc lamp, however, which will illus- 
trate the principles involved very nicely. 

The arrangement of the lamp is shown in the accompanying 
figure. W is a wooden baseboard about 5 inches square. 
Near one end and on the center line of the base mount a 
square upright post P, 3 inches high and % inch square. To 
the upper end of this post is to be secured two flat pieces 
of brass shown at R, about 1 inch long, and projecting above 
the top of the post about % inch. These pieces are to form 
a support for a brass lever L, which is swung on a pivot 
which has a bearing in the strips R. This lever is 3% inches 
long and the pivot is iy 2 inches from the left-hand end of 



EASY ELECTRICAL EXPERIMENTS. 



161 



the lever. It may be made from a piece of sheet brass 1-16 
inch thick and % inch wide. 

In order to •support the carbons there will be needed two 
small brass sockets shown at C. These are made by taking 
a piece of very thin brass and curling it up into the form 
of a very short tube % inch long and % inch in diameter. 

At S is a piece of brass 1/16 inch thick, bent into the shape 




The Are Lamp 

«hown, and secured to the post at the bottom, so that the 
outer end of the spring projects 2 inches from the post. 

Near the outer end of the lever L and the spring S solder 
one of the little brass sockets just described. They should 
be equal distances from the post P when the lever L is 
horizontal. 

Make a small lead weight, preferably in the form of a 
ball, as shown at B, provided with a hook so that it may be 
hung on the outer end of the horizontal lever. The lever 
should be so nicely pivoted that it swings very freely up 
and down. Take a piece of ordinary electric light carbon 
such as may be picked up in the street and break off two 



162 EASY ELECTRICAL EXPERIMENTS. 

pieces about 1% inches long. Put these pieces in a vise and 
file them down until they are each about y s inch in diameter. 
Then insert them in the two sockets and the arc lamp is com- 
plete. The weight B should be so adjusted that it almost 
balances the weight of the carbons and lever, but not quite. 
Connection is made by wires running to R and S. A suitable 
battery for use with this lamp will be described in the next 
paper. 



EASY ELECTRICAL EXPERIMENTS, 



163 



CHAPTER XLIX. 



AN EXPERIMENTAL BATTERY. 



In order to run the arc lamp described in the previous 
chapter, a battery will be required capable of giving a rather 
high electro motive force and a considerable current. At 
least ten cells ought to be used, and if we try to construct 
bi-chromate or similar cells we would find it a costly and 
troublesome task. A simple storage battery may be easiljr 



< 

i® ® ® ® ® ® ® 
j B ® 3® ® ® ® ® 


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1 

® S 


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Simple Storage Battery 



constructed which is capable of doing a number of interest- 
ing experiments and the cost is insignificant. 

The jars for containing the fluid for our storage battery 
are made of empty horseradish bottles. The amateur can 
arrange to make as many cells as he sees fit, but at least 
ten will be required for our experiment. They are arranged 



164 EASY ELECTRICAL EXPERIMENTS. 

in a long wooden trough shown at H in the accompanying 
figure. This trough is provided with upright strips at the end 
about ten inches high, across the top of which is a smooth 
flat board. The material of which this trough is made should 
be at least % inch thick. 

Each cell is composed of two strips of thin sheet lead 
immersed in a solution of sulphuric acid. The strips of lead 
are about % inch wide and are long enough to project 2 
inches above the top of the bottle. These are shown at K. 
To the upper ends of these strips are soldered pieces of cop- 
per wire such as bell-hangers ordinarily use. These wires 
are for the purpose of making connections with the various 
•cells. The strips of lead are prevented from touching each 
other by a strip of wood which fits tightly in the center of 
the neck of the bottle and is long enough to touch the bottom. 
The liquid used in the cell is a solution of sulphuric acid in 
water. The proper proportion is one part of acid to twelve 
parts of water, and the mixture should be made by pouring 
the acid slowly into the water. The bottles should then bp 
filled about % full of the liquid, the lead strips inserted, and 
the wooden strips pushed into place between them. 

We are now ready to arrange the connections of our bat- 
tery. On the top of the wooden strip are mounted small 
copper washers as shown at A and B. These copper washers 
are arranged in two rows of ten each, and are secured by a 
small screw passing through the washers into the wooden 
strip. The terminals of cell No. 1 are connected to A and B. 
The terminals of cell No. 2 are connected to C and D, and the 
other cells are connected in a similar manner. When all con- 
nections are made the cells are ready for charging. 

In connecting the cells for charging, all the copper washers 
in one row should be connected together by a strip of thin 
sheet copper and this strip is then connected to one terminal 
of a battery of three gravity cells connected in series. The 
other row of washers is similarly connected together by a 
second strip of copper, and this strip is connected to the 
other terminal of the gravity battery. An inspection will 
show that the cells are then all connected in parallel, and 
three gravity cells ought to give them a sufficient charge in 
one week, at the start. After this first charge they will 
charge enough over night to do considerable service the next 
day. After the cells are charged, the cells are all connected 
in series. This is done by removing the two copper strips 



' EASY ELECTRICAL EXPERIMENTS. 165 

just mentioned, and by connecting posts B and C, D and E, 
etc. When the cells are thus arranged in series, the electro- 
motive force of each cell is added to its neighbor, and the 
combined electro-motive force of the whole battery is con- 
siderable. The capacity of the cells as constructed is not 
very great— that is, they will not yield a current for a great 
while at a time, but nevertheless, many interesting experi- 
ments may be performed by their aid. 



i66 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER L. 



HOW TO MAKE AN ELECTRIC BOMB. 



When a mixture of an inflammable gas is ignited there 
results a violent explosion. This is made use of in the 
gas engine, so common at the present time. There must 
always be both air and gas 
present in the mixture, or there 
will be no explosion, on the 
same principle that a fire will 
not burn unless it can have air. 
Moreover, it is found that there 
must be a definite relation be- 
tween the amounts of air and 
gas, to secure the best results. 
It is found that with ordinary 
illuminating gas, the proper pro- j 
portions are 7 parts of air to 1 
part of the gas. A mixture dif- 
fering slightly from the above 
will explode fairly well, but no 
great variation from the above 
proportions is possible. 

The mixture may be exploded 
by contact with a flame, or bet- 
ter still, by passing through it 
an electric spark. Both of these 
methods have been made use of 
in the gas engine, although the 
use of the electric spark is fast 
superseding all other methods. 
The present chapter deals with 
the construction of a small electric bomb, which illustrates 
many important principles. 

Take piece of ordinary iron pipe, 4 inches long and 1^ 
inch in outside diameter. Turn the ends off smooth and 
true, and fit to one end an ordinary wooden plug, about 
% inch thick. This plug should fit tightly, and should be 
turned out in a lathe, and it is well also to turn out the 




VS///S/////////SP77& 



EASY ELECTRICAL EXPERIMENTS. 167 

inside of the pipe where the plug is to fit in, in order to 
ensure a perfect fit. 

Through the plug insert two short pieces of stiff brass 
wire, about two inches in length, bending the inside ends 
of these pieces toward each other, so that there is about 
% inch clear space between them. Then insert the plug 
in place, first brushing it over with a layer of shellac, and 
fasten it in place by means of screws passing through the 
pipe and into the plug. 

The bomb is now ready for filling with the explosive mix- 
ture. The surest way of doing this is indicated in the 
accompanying figure. Fill the pipe with water, and holding 
a piece of paper or the palm of the hand over its mouth, 
invert it in a dish of water, the mouth being submerged. 
Then remove the piece of paper, and if the plug at the top 
fits tightly, the bomb will remain filled with water, even 
though inverted. Attach a rubber tube to a gas jet, and 
place the open end of the tube in the water, and directly 
in the mouth of the inverted pipe. 

Upon turning on the gas, bubbles of gas will rise through 
the water, the level of the latter will fall in the tube, and 
of course the outer containing dish will fill up. These opera- 
tions cannot be seen through the pipe, and it may be well 
to take an ordinary horse-radish bottle, and experiment with 
that, just to see what takes place. 

When the pipe is y 8 full of gas, the latter should be turned 
off, and air forced into the pipe. The experimenter can tell 
how full the pipe is, by observing the rise in level in the 
water in the outer dish. A preliminary trial will enable 
the experimenter to tell just how much the level must rise in 
order to fill the pipe to any given height. 

When forcing in air, use a bicycle pump, as. the use of 
the lungs will force in a lot of carbonic acid gas, which will 
hinder combustion. 

Having filled the bomb, hold it with its mouth still under 
water, and insert a rather tight fitting cork. It may then 
be removed from the water, but if the cork does not fit 
tightly, it must still be kept bottom side up. 

If the two wires A and B are connected with the ter- 
minals of an induction coil capable of giving a % inch spark, 
the passage of the spark will ignite the mixture, producing 
a violent explosion. The experiment can be varied by using 
powder instead of gas, but of course the explosion of a bomb 



i68 EASY ELECTRICAL EXPERIMENTS. 

of this size filled with powder would be exceedingly dan- 
gerous. 

The two terminals, A and B could be connected by a piece 
of very fine wire, so small that it would be heated very hot 
by the passage of a current from a battery. In this case no 
induction coil would be needed, but considerably more labor 
is involved, as the wire will have to be replaced each time. 
Both of these methods are made use of in the construction 
of submarine mines in time of war. 



EASY ELECTRICAL EXPERIMENTS. 



169 



CHAPTER LI. 



HOW TO MAKE AN ELECTRIC ENGINE. 



The present chapter deals with the construction of a small 
electrical engine, which, while it is a toy, will be a source 
of amusement to the mechanically inclined youth. All the 
difficult parts of the machine may be obtained by dismantling 
an old brass clock. A wealth of material is available from 
such a source in the form of wheels, pinions, shafts and 
6trips of brass and of steel. 

A side view of the engine is given in Fig. 1, and a plan 
view is given in Fig. 2. At the left in Fig. 1, is shown an 
electromagnet. This is made from a round piece of iron 
rod, % inch in diameter, bent into the shape of the letter 




U, each of the arms being 3% inches long, measured from the 
extreme bottom. On each arm wind a coil of insulated wire, 
so as to form a bobbin 2 inches long and 1% inches in diam- 
eter. These had better be made of number 24 double cotton 
covered magnet wire of which about 4 ounces will be re- 
quired. Carefully insulate, the iron core by a layer of paper, 



170 



EASY ELECTRICAL EXPERIMENTS. 



before winding the wire, and provide also circular wooden 
ends for the coil, which fit tightly upon the iron core, and 
hold the wire in place. The end of core should project % 
inch beyond end of coil. 

Make a base board by taking a piece of smooth pine, or 
whitewood, % inch thick, 6% inches long and 35^ inches 
wide. Across each end screw two strips to keep the base 
from warping. Mount the magnet so that its center is 1% 
inches from the left hand end of the base, securing it in 




place by a block screwed to the base, the lower part of the 
iron core being fitted into a slot cut in the base. 

At a distance of 2% inches from the same end of the 
board, and in the center, mount very firmly a post, 2% inches 
high and y 2 inch square. This is shown at P. 

Having procured an old clock, cut with a file, two strips 
of brass, these strips being cut from those portions of the 
frame which hold the little steel bearings upon which the 
balance wheel rests. These strips should be one inch long, 
and cut so that the bearing is % inch from one end. Screw 
these strips to the opposite sides of the square post, so that 
the bearings are exactly 2% inches above the base board, 
and exactly in line. 

The beam shown at B is 3 inches long, and % inch wide. 
At one end, the strip is twisted around at right angles, by 



EASY ELECTRICAL EXPERIMENTS. 171 

damping securely in a vise, and twisting it with a wrench, 
placed at a distance of Y2 inch from the end. 

At a distance of 1% inches from this end, is to be fixed 
a pivot which is to fit exactly into the two bearings in the 
top of post P. Possibly a strip of brass may be cut out 
from the frame of the clock, which will have a hole in it 
at just the right place. Drive the balance wheel off from 
its shaft, and drive the latter tightly into place in the hole 
B, and adjust by filing, until the beam may be mounted in 
its bearings and swing very freely up and down. 

At the twisted end is to be mounted strips of soft iron 
shown at A, cut so as to fit as closely as possible into the 
space between the two limbs of the magnet, when the beam 
moves up and down. 

At the right hand end of the beam is to be pivoted an 
arm N, which is to take hold of the crank upon the shaft of 
motor. This arm is 1% inches long and should move very 
freely. The pivot which holds it should be very freely fast- 
ened to B, soldering it if necessary. 

The wheel W may be made by taking one of the larger 
wheels of the clock, and casting a lead rim around it. Be- 
cause of lack of space the amateur will be left to his own 
devices to accomplish this. 

The shaft upon which the wheel is mounted turns in two 
upright pieces of brass shown at H. The center of shaft 
should be V/s inches above the base, and is at a distance of 
4 7-16 inches from the left hand end of the base. The crank 
has a throw of % inch. 

At the back side of the shaft is mounted firmly a piece of 
of brass cut in the shape shown at K. This piece has bear- 
ing upon it a spring S, so adjusted that the electric circuit 
through the coils is closed while the armature A is moving 
downward, but opens the circuit as soon as the armature 
reaches its lowest point and begins to move upward. Thus 
the magnets are excited, and pull on the armature while it 
is moving downward, but cease to pull while it moves up- 
ward. Some adjustment of the contact strip K may be 
necessary at first, but it may then be soldered permanently 
in place. Three cells of gravity battery ought to run the 
motor at a good rate of speed. 



172 EASY ELECTRICAL EXPERIMENTS. 



CHAPTER LII. 



AN AUTOMATIC CIRCUIT CLOSER. 



Sometimes it is desirable to so arrange a curcuit, normally 
open, that when once closed it shall stay closed even though 
it be opened again at one point. For instance, an electric 
door bell may be so arranged as to ring continuously when 
once the push button is pressed even though the pressure is 
but instantaneous. Or, an electric alarm clock may be de- 
sired to work in conjunction with an ordinary electric bell 
so that the alarm once started will ring continuously unless 
stopped by some one. 

One way of accomplishing these results is to use an auto- 
matic circuit closing device such as is shown in the accom- 
panying sketch. Take a piece of %-inch board 4 inches wide 
and 5% inches long. Upon this board is to be mounted an 
electro magnet shown at M. This magnet is so simple that 
directions for building it will not be given. Its principal 
dimensions, however, are as follows. The length between 
centers of cores is V/ 2 inches, the length of core is 1% inch, 
the diameter of the latter is % inch and the outside diameter 
of coils is 1 inch. They are wound of No. 32 double silk 
covered magnet wire. Fine wire is used so that the magnet 
will have a high resistance for a reason that will be explained 
later. The center of the magnet is 2% inches from one end of 
the board and about % inch clear space is left between the 
back of the magnet and the edge of the board. 

At N is a soft iron armature about 3-32 inch thick. It is 
fastened to a thin brass spring shown at K. As will be seen, 
this spring projects about 1% inches beyond the armature 
and is supported at its outer end by being screwed to the 
wooden block P. At its upper end the brass spring is bent up 
into a peculiar hook projecting about 3-16 inch outward from 
the middle of the armature. 

Next provide a brass lever shown at L, about 2% inches 
long, y 8 inch thick and *4 m ch wide. This lever is pivoted at 
O, at a distance of about 1% inches from the nearer end of L. 
This is accomplished by boring a small hole through the piece 
and passing a screw through this hole into a block supported 



EASY ELECTRICAL EXPERIMENTS. 



173 



upon the wooden base. The lever should be so located upon 
the base that its end rests upon the hook shown at T when 
the armature N is farthest from the magnet core. When the 
armature is drawn toward the core, however, the lever L 
should slip from the hook and strike against a screw S which 




The Automatic Circuit Closer 

is supported by a strip of brass bent over at right angles and 
fastened to the base board. 

Five binding posts are provided in the position shown and 
the connections for the various parts of the apparatus are 
shown by lines. The bell to be rung is attached at the top, 
the battery is connected to the posts C and D, and the push- 
button, or other circuit closing device is connected to posts 
C and F. It is assumed that the apparatus is to be supported 



174 EASY ELECTRICAL EXPERIMENTS. 

in a vertical position. If connections are made as just indi- 
cated, the pressing of the button connecting C and F will send 
a current into the binding post D, from there through the 
magnet to the binding post F, thence to C, and to battery 
again. This will draw the armature N toward the magnet 
and allow the lever to fall against the screw S. The current 
will then have another path from the post D to B, through the 
bell to A, from A by means of the lever L to S, thence to the 
binding post C and battery. This will cause the bell to ring 
continuously, even though the connection between C and F 
be broken. The ringing can be stopped by pulling down on 
the projecting part of the lever L. 

An ordinary alarm clock may be easily arranged to close 
an electric cuircuit when its own bell rings, and this in turn 
may start another bell by means of the device just indicated, 
which will ring until stopped by some one. 

The device might also be applied in a very simple manner 
to a burglar alarm system. 



EASY ELECTRICAL EXPERIMENTS. 175 



CHAPTER LIII. 



A MODEL FIRE ALARM TELEGRAPH, 



PART ONE. 

All modern fire alarm systems depend for their action 
upon some form of clockwork, which in connection with 
die electric current, operates the bells or whistles which 
give the alarm. This might be done in two ways— either 
by causing the clock-work to close an electric circuit in a 
special manner, causing the bells to sound each time that 
the circuit is closed, or by employing the clock-work to 
break an electric circuit, normally closed, the breaking of 
the circuit causing the bells to strike. This is the method 
usually employed in modern systems, for the reason that 
if a wire breaks or any part of the circuit is accidentally 
opened, the break is noticed at once, and can be immedi- 
ately repaired. 

It is easy to make a model fire alarm system using the 
works of an ordinary brass clock. This chapter and the 
following, will describe now to make such a model. On 
account of the varying sizes met with in different clocks, it 
is hard to give exact dimensions, but the ingenious reader 
will easily grasp the main principles, and modify his model 
to suit the material on hand. A diagram is given below. 
In this diagram the frame-work and wheels of a simple 
clockwork are sketched. It is better to use a clock which 
is provided with a spring and train of wheels for striking 
the hour, but the description given assumes that this is not 
available. 

Carefully remove the balance wheel and escape lever from 
the clock. As soon as this is done, the clock will immedi- 
ately run down at high speed unless care be taken to secure 
the wheels so that they cannot turn. The first thing to do 
is to fasten a vane to the shaft of the smallest wheel re- 
maining, such as is shown at V in the figure, the action 
of which is to prevent the clock from running down too 
fast. This vane may be made of very thin copper or brass.. 



176 



EASY ELECTRICAL EXPERIMENTS. 



and need not be fastened very firmly to the shaft, the only 
requisite being that it shall not slip on the shaft when the 
latter turns. It should be of such size that the shaft which 
carries the minute hand of the clock, (that is the long 
hand), shall make one revolution in about half a minute. 

Remove the gear wheel which carries the shorter hand 
of the clock, and fasten to the shaft which ordinarily car- 
ries the minute hand, a brass disc shown at D in the figure. 
This disc is 2 inches in diameter, and at least 1-16 inch 




Clockwork Mechanism of Fire Alarm 

thick. Notches are cut in this disc as shown, the notches 
being 3-16 inch wide, and the space between them is of the 
same width. Starting at the part of the disc which is 
uppermost, cut three such notches, properly spaced, then 
leave a space of %-inch and cut four notches, then another 
space of % inch, and finally cut two notches, giving the disc 
the appearance shown. 

Cut out two discs like that shown, at W, % inch in diam- 
eter, and 1-16 inch thick. One of these is to be secured 
to the main driving shaft of the clock, the other to the 
shaft of the clock, the other to the shaft which carries the 
disc D. They should be so fastened that the notches which 



EASY ELECTRICAL EXPERIMENTS. - 177 

are cut in them shall stand exactly vertical above their 
respective shafts, at the same instant of time. These discs 
must be firmly fastened in place, preferably by soldering. 

A hook shown at H must now be made, from a piece of 
rather stout brass wire. This hook is secured by soldering, 
to a straight piece of brass rod, which is cut of such a 
length that it may be pivoted in the frame work of the 
clock, as shown at 0. To this shaft are secured three other 
arms, which may be of light brass wire, in substantially 
the position shown. 

The object of the three peculiar arms is this. Arm No. 1 
is designed to strike against the vane V on the small wheel 
of the clock, preventing the wheels from turning. Arm No. 
2 is designed to drop into the slot on the middle wheel of 
the clock, when the slot is in a vertical position relative to 
its shaft. Arm No. 3 is designed to fall in a like manner 
into the slot on the main shaft. Now if the two discs have 
their slots vertical at the same time, the arms No. 2 and 
No. 3 will fall into their respective slots, and arm No. 1 
will strike against the vane, preventing the clock work 
from turning. If, however, the hook H be pulled down, 
arm No. 1 should clear the vane V, the wheels should turn, 
and arm No. 2 will ride on the edge of its disc, while the 
shaft K turns. 

When the shaft K has made one revolution, the arm will 
try to drop into its slot, but will be prevented from doing 
so because arm No. 3 cannot fall. The clockwork will turn 
until both slots again become vertical. 

At A is secured a block of wood, and fastened to it is the 
spring S which bears firmly against the surface of the wheel 
D, except when a slot passes under the spring, when the 
latter should break contract with the disc. 

The remainder of our apparat^ will be described in the 
following chapter. 



i 7 8 EASY ELECTRICAL EXPERIMENTS. 



CHAPTER LIV. 



A MODEL FIRE ALARM TELEGRAPH 



PART TWO. 



In the preceding chapter we described the arrangement of 
train of clockwork, so designed as to interrupt an electric 
circuit in a regular manner. This clockwork was arranged 
to be set into motion by means of a hook, which was to be 
pulled down in a manner similar to the fire alarm boxes used 
in all cities. The amateur can easily design a box for 
himself, to hold this clockwork, with the starting hook pro- 
truding from one side. In this chapter we shall see how to- 
make a bell to work in conjunction with the clockwork. 

First of all we shall need a piece of thin sheet iron, very 
soft, whose length is 3% inches, width 3 inches, and whose 
thickness in 1-16 inch or thereabouts. This is bent over at 
right angles at a distance of 1% inches from one end, as 
shown at I in the accompanying figure. This piece of iron 
serves as a support for two coils of wire upon iron cores, 
forming an ordinary electro-magnet. A side view of this 
magnet is shown in the figure. The iron cores are % inch in 
diameter, 2% inches long, and are spaced so that their centers 
are 2 inches apart, and at a height of % inch above the bot- 
tom of the iron strip first mentioned. Drive tightly upon the 
iron cores some circular brass heads, one close to each end, 
to hold the magnet wire in place which is to furnish the 
exciting power to ring the bell by means of an electric 
current. The brass heads are l 1 ^ inches in diameter. Having 
carefully covered the iron cores and the brass heads with 
heavy paper, so as thoroughly insulate them, wind each bob- 
bin full of No. 24 double cotton covered magnet wire. Abotit 
y 2 pound will be required for the two spools. 

An iron armature shown at A must be provided, consisting 
of an iron strip 2% inches long, % inch wide, and of anv 
convenient thickness. It is fastened transversely at its cen- 
ter to a small strip of brass, shown at K, wnose length is. 



EASY ELECTRICAL EXPERIMENTS. 



179 



1% inch, and is thick enough to be quite stiff. This strip 
is pivoted between two small upright supports one of which 
is shown at F. When exactly vertical, the strip K should 
leave a clear space of 1-64 inch between it and the iron 
cores, this space being left so that the ends of the cores may 
be covered with small pieces of paper glued in place with 
shellac. These pieces of paper are to prevent the armature 
from touching the cores. 

At D is a stiff piece of brass, which serves two purposes. 




Fire Alarm Telegraph. Bell 

First it serves as a support for the spiral spring S, which 
draws the strip K toward the left. Secondly, it serves as a 
stop for strip K, preventing it from going too far toward the left. 
To the upper end of K is fastened a wire, which carries 
at its upper end a rather heavy piece of brass, to serve as 
a hammer for the bell B. The amateur will be able to secure 
an old gong of some kind, perhaps from a clock. As the 
dimensions of these bells will vary, the reader will have to 
adjust the position of the hammer H, and the gong, to suit 



i8o EASY ELECTRICAL EXPERIMENTS. 

his individual case. When the strip K moves to the left, 
and brings up against the end of D, the hammer H should 
just barely clear the inside of the bell. Then when the ham- 
mer moves swiftly, its momentum will be sufficient to cause 
it to strike the bell sharply, and then bound back, allowing 
the bell to give a sharp, clear tone. 

The supporting base for the whole arrangement is made 
of a piece of smooth pine or whitewood. The post P is 
mortised firmly into the base, passing between the coils of 
wire. The post is about 4% inches in height. 

The bell and clockwork are to be joined in series with three 
cells of gravity battery. Connection is made with the in- 
sulated spring on the clockwork, and to the brass frame of 
the same. As arranged, the number of the box to be struck 
is 243. When the circuit is closed by the clockwork, the 
armature A should be drawn against the cores. When the 
circuit is broken, it should spring away, striking a sharp 
blow on the bell. 



EASY ELECTRICAL EXPERIMENTS. 



181 



CHAPTER LV. 



HOW TO MAKE A LARGE INDUCTION COIL. 



PART ONE. 



While the induction coil to be described in the following 
chapters would not be classed as a large coil by manv manu- 
facturers, yet it is much more powerful than the amateur 
ordinarily meets with. It is capable of furnishing a spark 
four inches in length, representing an electromotive force of 
something like 160,000 volts. Such a coil will excite an X-ray 
tube quite well, and will operate satisfactorily in wireless 
telegraph work also. 

It is assumed that the reader is already familiar with the 
essential parts of an induction coil. As is well known, such 
a coil consists of a primary, surrounding an iron core, and a 
secondary coil surrounding both the primary and the core, 









A 


C 




r n 


Pis. 1. 


„/ 


r 



but securely insulated from both. In our coil, the principal 
difficulty will be to properly insulate the secondary coil, 
against the high voltage generated within itself. 

To make the primary coil, we shall need first, a smooth, 
firm core composed of a bundle of soft iron wires, 12% inches 
long and % inch in diameter. The separate wires composing 
this bundle should be about No. 20 B. & S. gauge, and 
should be very soft and straight. Fit tightly to the ends of 
this bundle two wooden ends, made by turning from maple 
or other tough wood, two thimbles of the shape shown at A 
and B in Fig. 1. Each end-piece is 1 inch in length, %-inch 



182 EASY ELECTRICAL EXPERIMENTS. 

in external diameter, and %-inch in internal diameter. They 
should slip tightly upon the iron core. As this involves quite 
a stress upon the ends, it may be well to turn two or three 
grooves in the outer surface of each, in which strong bind- 
ing strings may be wound, to prevent splitting. 

Now cover the central portion of the core with a layer of 
paper, fastened on with shellac. Then wind in this space 
two layers of No. 16 double cotton covered magnet wire. 
This will make a primary coil whose external diameter i& 
%-inch, and whose length is 12% inches. 

Secure from a stationer, one of the ordinary tubes used for 
sending pictures through the mail. This tube should be 1% 
inches in external diameter, and of the same length as the 
core. We wish to secure the primary coil, with its core, in 
the center of the pasteboard tube, and there to fill the inter- 
vening space with an insulating mixture. Accordingly the 
tube should be closed at one end by a piece of heavy paste- 
board glued in place, and then held in a vertical position, 
with the closed end downward. 

Carefully insert the primary coil into the center of the 
tube, while vertical, and then pour into the tube, a mixture 
made up of melting 4 pounds of rosin with 1 pound of bees- 
wax. This mixture should be poured in hot, and the tube 
left undisturbed until it is cold. However, when the mix- 
ture cools it contracts, and as fast as it contracts mor mix- 
ture must be poured in so asi to keep the tube full. When 
these operations are complete, we shall have a primary coil 
completely encased in a layer of wax, except at the ends, the 
whole being encased in a pasteboard tube. The latter should 
be given a thorough coat of shellac, and set aside to dry. A 
section of the finished primary is shown in the lower part of 
Fig. 1. The ends of the coil should project from one end for 
a distance of about six inches. 

In our next chapter we shall describe how to make the 
secondary of our coil. 



EASY ELECTRICAL EXPERIMENTS. 



183 



CHAPTER LVI. 



HOW TO MAKE A LARGE INDUCTION COIL. 



PART TWO. 



In the previous chapter directions were given for the con- 
struction of the primary of our coil. The secondary will next 
receive our attention. The primary consists of a compara- 
tively few turns of coarse wire, while the secondary consists 





of a very great number of turns of fine wire. Each turn of 
the secondary has generated within it an electromotive force, 
and as the latter must be very high, this necessitates a large 
number of turns. 

The secondary cannot be wound in one large continuous 
coil. If we did this, the electromotive force would be so 
great as to strike through the silk insulation upon the wire, 
rendering the coil inoperative. The coil is made up of a num- 
ber of disk-like sections such as is shown at the left in Pig. 
2. The sections are placed side by side, with insulating ma- 



184 



EASY ELECTRICAL EXPERIMENTS. 



terial between them, and each section is connected in series 
with the next, so that the effect is the same as if the coil 
were wound in the ordinary manner. 

In order to wind the sections a special winder will be re- 
quired. A suggestion as to the method of construction is 
given in Fig. 3. A and B are two circular pieces of wood, 
3% inches in diameter. Between them is another circular 
piece 1% inches in diameter and 3-16 inch thick. The three 
pieces are tightly screwed together, with their centers coin- 
cident. The inner faces of A and B, and of the center piece, 
must be smooth and true, so that when the screws are tight- 
ened up the three pieces will fit perfectly together. They 
are to be mounted upon a shaft supported in suitable bear- 



"vj 



Fig. 3 



KJ 



ings and provided with a crank, so that wire may be wound 
upon the central portion. The disc A may fit loosely upon the 
shaft, but B should fit tightly so as to turn with the shaft. 
For this reason B should be rather thick and should prefer- 
ably be of hard wood. The disc in the cutter should be 
tapered, the smaller end being next to A, so as t& permit 
the coil, after it is wound, to be easily removed. 

Having made this rather crude winding device, we are 
ready to wind the sections of the coil. For this purpose we 
shall need about 6 pounds of No. 34 single silk covered mag- 
net wire. Each small section consists of 1,500 turns, wound 
as tightly and as evenly as possible. 

In winding, support the spool upon which the wire is 
bought in some convenient place, and arrange it so that the t 



EASY ELECTRICAL EXPERIMENTS. 185 

wire, in passing from this spool to the winder, shall dip into 
a dish containing melted paraffine wax. This can be done 
by using a rather deep dish for melting the wax, with a 
spool immersed in the melted wax, under which the wire 
runs in passing to the winder. 

Using the apparatus shown in Fig. 3, wind eight sections, 
each having 1,500 turns. Each section as it is wound can be 
carefully removed from the winder without damaging the 
turns of wire. To prevent the coil from sticking to A and B, 
two thin disks of paper may be placed against the inner 
faces of the pieces, and may be lightly glued to A and B 
at three or four points around the edge. 

After each section is removed wrap a strip of thin tissue 
paper around the coil at three or four points, fastening the 
strip by a bit of wax to prevent the coil from unwinding or 
losing its shape. 

Having made eight sections of the dimensions given above, 
remove the disc in the center and substitute therefor another 
disc two inches in diameter and slightly tapered as before. 
This will make a section with a larger hole in the center, 
but exactly like the preceding in general shape. Then make 
18 of these sections, each section being of 1,000 turns. 

We will continue our discussion in the following chapter. 



i86 



EASY ELECTRICAL EXPERIMENTS. 



CHAPTER LVII. 



HOW. TO MAKE A LARGE INDUCTION COIL. 



PART THREE. 



F.g4 



After the various sections of the induction coil are wound, 
as described in the last chapter, they must be connected to- 
gether or "stacked." Each section is connected in series with 
its neighbor, and the turns are so con- 
nected that the current will go around 
each section in the same direction. Be- 
tween the sections are two rings cut 
from heavy manila paper, the outer diam- 
eter of the rings being four inches. Three 
rings separate the sections, and prevent 
a spark from passing between the sec- 
tions. 

Take a piece of board about % inch 
thick, and cut a circular piece 4% inches 
in diameter. Through the center bore a 
hole, which shall be large enough to ad- 
mit the pasteboard tube containing the 
primary, and make a tight fit. This 
piece of wood is seen at J> in Fig. 4, with 
the tube projecting at T for a distance 
of three inches. 

The method of stacking the sections is 
indicated in Fig. 3 of the preceding 
chapter. Beginning with the bottom 
section, lay upon it one of the paper 
rings already mentioned. The bottom section should be one 
of the eighteen sections of 1,000 turns. Cut a little slit in 
the edge of the paper ring, in as far as the wire, and through 
this slit pass the terminal of the wire. Now on top of this 
lay another paper ring, with its slit turned around so as to 
be 90 degrees from the first slit. On top of this place the 
second section, passing its terminal through the proper slit, 
and connecting it to the terminal of the first section with a 
small, soldered joint. Proceed in a like manner with all the 




EASY ELECTRICAL EXPERIMENTS. 



187 



sec'tions, taking care to have two paper rings between each 
section, and to have the joints between the wires as far from 
each other as possible. 

The "stacking" is to be begun upon the board D, Fig. 4, 
as a base, the sections being piled up around the primary. 
Between the first section and D is to be placed a wooden 
ring whose outside diameter is 3% inches, and whose thick- 
ness is % inch. After piling up nine of the smaller sections, 
insert another wooden ring whose thickness is % inch. Then 
put the larger sections (those containing 1,500 turns) into 
place. Above these place another wooden ring % inch thick, 
and above this the remainder of the 1,000 turn sections. The 




Fig. 6. 




wooden rings used should be thoroughly dried in an oven 
and then well soaked in boiling hot paraffin wax before being 
used: 

The two terminals of the finished secondary may be 
brought out at the ends, one through a small hole in D, the 
other being left sticking straight upward. Now select a piece 
of heavy wrapping paper, and of it make a stiff tube which 
shall surround D and the coils which it supports. This tube 
is to be filled with melted wax, so it must make a tight joint 
with D. A string wrapped tightly about it will help make 
the joint tight. 

Now make up a mixture by melting together four pounds 



188 EASY ELECTRICAL EXPERIMENTS. 

of rosin and one pound of beeswax. When this mixture is 
hot, pour it into the tube containing the sections. A heavy 
weight should be placed on the sections to keep them from 
floating, which may be removed when the wax is nearly 
solidified. The wax should extend above the top of the sec- 
tions for a distance of % inch. As the wax cools it contracts, 
and more hot wax must be added from time to time. 

A section of the finished secondary is shown in Fig. 6, the 
primary being removed. The outer paper tube, as well as D, 
is removed, as they are only temporary. Also the wooden 
ring nearest D is removed by chipping away the wax, ani 
its place filled by pouring in hot wax. 

One of the interior wooden rings is indicated at W. 



EASY ELECTRICAL EXPERIMENTS. 189* 



CHAPTER LVIII. 



HOW TO MAKE A LARGE INDUCTION COIL. 



PART FOUR. 



Having made the primary and secondary coils, they must 
next be mounted in a suitable framework and provided with 
some form of interrupter for making and breaking the pri- 
mary current. 

The supporting framework should preferably be made of 
well-seasoned mahogany, although any wood capable of tak- 
ing a good finish will do. A base should first be made 
whose length is 18 inches, and which is 8 inches wide. To 
prevent warping, it is best to dovetail a strip of wood across 
each end, or else make the base of two boards glued and 
screwed together, with the grains of the pieces at right 
angles. 

Two upright pieces of wood will be needed, each five inches 
square and three-fourths of an inch thick. Through the cen- 
ter of each bore a hole which will just fit the primary tube. 
Then the latter may be slipped into the upright pieces, one 
at each end, and the uprights screwed to the baseboard, thus 
securing the coil firmly to the base. The position of the coil 
is shown in fig. 7. 

The binding posts should be provided to receive the ter- 
minals of the secondary. They should be mounted on two 
hard-rubber blocks, as shown at R, and then the latter are 
fastened to the upright strips. 

Two straight pieces of brass wire about 6 inches long,, 
shown at P, should be made. They should slip easily through 
the holes in the binding posts, but should, not be loose enough 
to "wobble." Each must be pointed at one end and provided 
with a handle of hard rubber at the other. 

An interrupter of the well-known hammer type is shown 
at the right. A rather limber brass spring is provided with 
an iron armature, H, the spring being of such a length that 
H is directly opposite the end of the iron core of the coil. 
The end of the latter should just come flush with the end of 



190 



EASY ELECTRICAL EXPERIMENTS. 



the tube. There should be about one-eighth of an inch space 
between H and the core. 

At D, about one inch below the center of H, a small hole 
is drilled in the brass spring, and a piece of small platinum 
wire riveted into the hole. The screw, B, which rests against 
D, is also tipped with platinum, and it is supported by a very 
stiff piece of brass. 

One end of the primary coil is connected to a binding 
post (not shown), and the other end to the spring which sup- 
ports H. Then B is connected to a second binding post on 
the base. 

When a battery of five bichromate cells (large size) is 




connected to the instrument, the hammer, H, should fly rapidly 
back and forth, breaking the primary circuit at D. 

In order to work well, however, a condenser must be 
bridged across the spark gap , at D. This condenser may be 
made by taking about 100 sheets of tin foil 5 inches by 7 
inches and stacking them up with a sheet of paraffined type- 
writer paper (thin) between them. Every odd numbered 
sheet is connected together, forming one terminal of the con- 
denser. The even numbered sheets, connected together, form 
the other terminal. The condenser should be clamped tightly 
together. 

When provided with a condenser as described, the coil 
should give a four-inch spark without difficulty. 



EASY ELECTRICAL EXPERIMENTS. 



191 



CHAPTER LIX. 



HOW TO MAKE AN ELECTRIC LOCOMOTIVE. 



PART ONE. 



Any ingenious boy can readily construct a model electric 
locomotive which will be the source of much pleasure and in- 
struction as well. 

The main outlines of the motor to be used are shown in 





Fig. ! 




Showing Outlines of Motor. 

the accompanying figure. It consists of three main parts, 
the field magnet M, the field coils H, and the armature A. The 
field magnet M is made up from strips of thin sheet iron, 
such as may be bought at any stove dealers. This iron is cut 
into strips about 9 inches long and 1% inches wide, and about 
eight strips of this size will be required. In order to bend 
these strips into the shape shown in the figure, it is best to 
make a wooden form the shape of which is exactlv the shape 
of the interior space between the limbs of the magnet. This 



192 EASY ELECTRICAL EXPERIMENTS. 

space is circular at one end as shown and the diameter of 
this circular space is 1% inches. The length of the interior 
straight portions is 2% inches. Clamp the wooden form in a 
vise and bend the iron strips around it one at a time, until 
they all conform exactly to the shape shown in the figure. 
Provide blocks of wood shown at B, of which the upper is 2^4 
inches long, the middle one being of the same length, and 
the lower one being 3% inches long. By means of brass 
screws passing from the upper and lower blocks into the 
middle block, the strips of iron may be tightly squeezed to- 
gether into a solid mass. 

The field coils shown at H are 1% inches long and surround 
the iron core to a depth of % inch. It is best to make up a 
small form from thin sheet brass or copper which shall have 
the dimensions of the finished coil, and upon w T hich the field 
coils may be wound and afterwards slipped into place. If 
this is done, however, the coils must be finished and slipped 
on before the circular space at the end of the magnet is 
formed. The wire used should be No. 24 double cotton cov- 
ered, and about 4 ounces will be required. Be very careful to- 
insulate all metal parts by covering them with a layer of 
paper before winding on the wire. The coils are connected 
in series in the ordinary manner. 

Passing now to the armature, we come to a more difficult 
matter. The shape of the iron part of the armature is shown 
at C. It consists of three parts— a rectangular central por- 
tion % i n ch thick, y% inch long and y% inch wide. To 
the narrow faces of this block are to be fastened the two 
circular end portions, by means of flat-head iron screws pass- 
ing through the outer pieces into the central block. These 
circular pieces of iron should be of such dimensions that 
when bolted together the armature should have an outside 
diameter of exactly 1 inch, and the length of these outer 
sections is 1% inches. Thus an iron core will be formed 
whose length is 1% inches, whose diameter is 1 inch and 
which has a groove % inch wide running lengthwise around 
the core. In the exact center bore a hole lengthwise through 
the core, % inch in diameter. Into this drive tightly a shaft 
2% inches in length and perfectly straight. Now w T ind the 
slot in the armature core full of No. 24 magnet wire care- 
fully insulated from the iron core. 

A commutator must now be made, shown at K, and con- 
sisting of a circular hardwood block % inch in diameter and 
5-16 inch thick, on the outer surface of which are fastened 



EASY ELECTRICAL EXPERIMENTS. 193 

two semi-circular pieces of thin copper. The method of 
fastening these is shown in the small figure at the right. 
The pieces of copper may be cut from any thin sheet, with 
the little tongues projecting as shown in the figure. The 
pieces of copper may then be bent into circular form so as 
to fit closely the wooden block, and may be fastened to the 
latter by bending the tongues down over the ends of the 
block, and secured by a pin driven through the tongues into 
the block. The block has a hole in the center just large 
•enough so that it will fit very snugly upon the shaft when 
put into the position shown in the figure. Care must be 
taken that the two sections of the commutator do not touch 
•each other, nor the iron shaft of the motor. The slot should 
be in the position shown— that is, at right angles to the 
groove on the iron part of the armature. Outside the com- 
mutator and separated therefrom is driven on a small gear 
wheel taken from an old clock. Each end of the armature 
winding is connected to one of the sections of the com- 
mutator. 

It will be noticed that no bearings or supports for the arma- 
ture are described, as this will be left for a following chapter. 



194 EASY ELECTRICAL EXPERIMENTS. 



CHAPTER LX. 



HOW TO MAKE AN ELECTRIC LOCOMOTIVE, 



PART TWO. 



The motor for our model locomotive was described in a 
preceding chapter. This motor must be mounted on a suita- 
ble truck, the construction of which will now be described. 
A general view of the truck and motor is shown in the accom- 
panying figure. The wheels shown at W are perferably 
turned from hard rubber, but may be turned from a piece 
of hard wood. The material required is y 2 inch thick, the 
running face of the wheel being % inch wide, the flange % 
inch and the small hub % inch thick. The diameter of the 
running face of the wheel is ls/% inches, the diameter of the 
flange is 2 inches and that of the hub is y% inch. They are 
mounted upon shafts made of a piece of 5-32 inch brass or 
iron rod threaded at each end so as to screw tightly into the 
wheels. The total length of this shaft is 3% inches, and the 
distance between the hubs of the two wheels is 2y 2 inches. 

The front and rear axles of the truck are connected by two 
brass strips E and D which are 5 inches long, % inch wide 
and y 8 in thick. 

The motor which was described in the previous chapter is 
mounted in the frame thus formed by screws passing through 
the brass strips and into the wooden block which is clamped 
between the limbs of the magnet. A similar arrangement of 
wooden blocks at the end of the magnet shown at M se- 
curely fastens the magnet in place. The long strip F should 
be on the lower side of the truck. 

Connection is made between the armature and the front 
shaft by means of the train of gears indicated at A, H and B. 
These gears may be taken from an old brass clock, and since 
the size of the wheels used must necessarily be different in 
each case, the exact distance between the shafts supporting 
these gears cannot be given. The amateur will have to begin 
by first locating the gear A, then the shaft which carries the 
gear H, then the shaft which carries B and the armature o£ 



EASY ELECTRICAL EXPERIMENTS. 



195 



the motor, and the location of this last shaft will determine 
the location of the field magnet frame in the frame of the 
truck. 

If the locomotive is to run on a straight track, the axles may 
be rigidly fixed as already described. If, however, it is run 
on a circular track, especially if the latter be of rather short 




Plan View of Truck 



radius, one of the axles will have to be so fixed that it may- 
swing in one way or the other to allow the locomotive to go 
around the curves. The amateur can easily arrange this for 
himself. 

The springs which convey the current into the armature are 
made of very thin spring copper or brass and are fastened 
to the wooden blocks so as to bear rather lightly upon the 
commutator C. They are omitted in the diagram for the sake 
of clearness. The armature and fields of the motor are con- 
nected in series, and the terminals of the motor are connected 
to two brass springs which are screwed on to the terminals 
of the wooden strip F, and are bent downward so as to bear 
upon the rails upon which the wheels are to run. The track 
may be made of strips of thin copper, cut into convenient 
length about 1 inch wide and bent over at right angles so as- 
to form a suitable bearing surface for the wheels. The rails 
serve as conductors for the currents of electricity and must 
therefore be fastened to some non-conducting support suctt 
as wood. 



196 



EASY ELECTRICAL EXPERIMENTS. 



The amateur may follow his own devices in the construction 
of the body of his model locomotive, the form shown in Fig. 3 
being a model of some of the large locomotives now in use. 
If the reader possesses a scroll saw, he may cut the parts nec- 




Electric Locomotive Complete 



essary to construct his model from pieces of thin wood which 
may afterward be glued together, and painted black, present- 
ing a very neat appearance. Four cells of bichromate battery 
ought to run the locomotive at a good rate of speed. 



EASY ELECTRICAL EXPERIMENTS. 197 



CHAPTER LXI. 



A PORTABLE VOLTMETER. 



PART ONE. 



Voltmeters are instruments for measuring the voltage, or 
electrical pressure, between two points of an electric cir- 
cuit. Some voltmeters are designed to be used in one posi- 
tion, while others are designed to be carried about, and to 
give essentially correct readings in any position. The latter 
are harder to construct than the former, but as may be read- 
ily seen, they have a wider range of usefulness. In the 
following chapters directions will be given for constructing 
a portable instrument, the form of construction adopted be- 
ing one that has been proved by experiment to be perfectly 
practical, and easily constructed by a person with few tools. 
There will be needed for the base of the instrument, a piece 
of well dried cherry 6% inches square and % inch thick. It 
is well to take considerable pains in finishing this up so as 
to make it perfectly smooth and true. The edges should be 
beveled, as shown in Fig 1. To this base is to be fastened, 
on its upper side, a block of wood 1% inches long, V/± inches 
wide and % inch high. This block is fastened by two heavy 
screws, as shown at W, and is so placed that the center of 
the block is on the center line of the base, and the outer 
edge of the block is % inch from the edge of the base. 

Now procure an ordinary 3-inch horseshoe magnet. This 
is to be secured firmly to the upper side of the wooden block 
by a clamp made from a piece of stiff sheet brass through 
which a screw passes into the wooden block, securely clamp- 
ing the magnet in place, as shown at M. 

We will now proceed to construct the movable part of 
our instrument. There will be needed first of all a large- 
sized sewing needle about 2 inches long. The eye-end of 
this needle should be broken off and ground to a fine point 
so as to make a needle V/ 2 inches long. We wish to secure 
to this needle a small thin piece of soft iron, as shown at 
I in Fig. 2. A very simple way to do this is to cut out a 



198 



EASY ELECTRICAL EXPERIMENTS. 



long narrow strip of thin sheet brass, such as is shown at 
P in Figs. 1 and 2. By means of two holes through this 
piece near one end, which are just big enough to allow the 
needle to pass easily, the piece of iron may be secured firmly 
in place and by forcibly bending the brass strip, the latter 
will bite the needle hard enough to prevent the whole from 
turning easily upon the needle. The upper end of this strip 




Is bent over at right angles at a distance of 5-16 inch from 
the upper end of the needle. The object of this bend is two- 
fold. First, it is to be used to support the pointer N by 
being bent around the latter, and for this reason the strip 
at this point should be cut rather wide, say % inch. Second, 
the weight of the projecting part of the strip is designed to 
counteract the weight of the pointer so as to form a moving 
system which will be nicely balanced. 



EASY ELECTRICAL EXPERIMENTS. 199 

To support the needle we will need a piece of brass about 
5-16 inch wide bent into the shape shown at S. The height 
of the under side of this brass support is about 1 3-16 inches 
above the base. A small block of brass is shown fastened t© 
tnis strip. This block serves as a support for a bearing 
made of glass which greatly diminishes friction. 

To make these glass bearings procure a piece of very 
small glass tubing such as chemists use. Insert one end 
into a gas flame and heat it until the end softens and runs 
together. If the tube be held vertical and allowed to cool, 
the outer end of the tube will be rounded and the inner end 
of the tube where it is closed up will taper down to a point. 
If now the end of the tube be cut off so as to form a piece 
about % inch long there will be formed a piece of glass 
something like that shown at G, Fig. 2. The glass tube may 
be cut by making a deep incision on one side of the tube 
with a sharp file. If the tube be held in the hands, with the 
thumbs held on each side of the scratch, the latter being 
on the opposite side of the tube, then the tube may be 
easily snapped off. Two such bearings will be required, one 
held in the brass block as already described, the other fas- 
tened into a recess in the wooden base, and held in place 
by a small piece of brass, B, screwed to the base. Of course 
holes must be bored through the brass strips, B and S, so 
that the needle may pass through them, but not large enough 
to allow the glass bearings tc slip out of place. 

The needle should be supported in smch a position as to 
pass vertically between the poles of the horseshoe macrnet 
at a distance of y 8 inch within the latter. The needle N is 
made from a slender straight piece of broom corn taken 
from an ordinary whisk broom, and is secured as has been 
explained by bending the end of P over until it clamps the 
needle. The needle may be made about 4 inches long at first. 

We will continue the discussion of this instrument in our 
following chapter. 



200 EASY ELECTRICAL EXPERIMENTS. 



CHAPTER LXII. 



A PORTABLE VOLTMETER 



PART TWO. 

In the previous chapter a description was given of the mov- 
ing parts of our voltmeter. It consists of a straight steel 
needle at the center of which is mounted a small thin bit of 
soft iron about % inch long, and % inch wide, and of a pointer 
attached at the top of the needle, made of a strand from a 
broom. The piece of iron and the pointer are secured by a 
small strip of brass as previously described, and the whole 
moving system suitably mounted in glass bearings so as to 
turn very freely. The strip of iron should be at such a height 
above the base board that it is half way between the latter 
and the .horizontal steel magnet. The magnet will then turn 
the iron strip around until it points along a line parallel to 
the pole pieces. The pointer should now be turned toward 
the left by bending the strip of brass until, with the iron 
strip in the position just described the pointer is bent away 
at an angle of about 30 deg. Referring to Fig. 4 the strip of 
iron can be seen at I, and the ends of the magnet pole at M 
with the needle passing vertically between them. In Fig. 3 
the position of the pointer relative to the rest of the instru- 
ment is shown at P. Having completed these adjustments 
the pointer and moving armature should be counter-balanced 
by filing, or bending the brass strip until tipping the instru- 
ment produces little change in the position of the needle. 
Care should be taken to see that the needle moves very freely 
and that the pointer P always returns to the same position 
after being deflected. 

In Fig. 3, there can be seen at C two coils of wire. These 
are made by winding the coils upon two brass frame works 
each of which consists of a rectangular spool with heads of 
the shape shown at C in Fig. 4. These heads are 1% inches 
long, % inch high and are made of thin brass. The shank of 
the spool is likewise made of thin brass and has an opening 
through its center % inch long and 3-16 inch wide. The pur- 



EASY ELECTRICAL EXPERIMENTS. 



20I 



pose of this opening is to allow the coils to be supported close 
to the moving armature and yet to allow a free space in 
which the strip of iron I may turn. The ends of the spools 
are soldered to the shank and together make up a spool which 
Is %-inch wide. On one side of each spool a lug is left pro- 




JJ 



jecting by means of which the spool may be screwed to the 
baseboard. 

Carefully insulate the whole interior surface of the spool 
and wind the same full of No. 36 double silk covered magnet 
wire. The spools are then mounted in the position shown in 
Fig. 3. They are connected together in such a way that the 
effect of one is added to that of the other and their free ends 
are connected to two binding posts A and B. The purpose of 
these coils is to receive the current to be measured. The 



202 



EASY ELECTRICAL EXPERIMENTS. 



effect of the current in the coils is to cause the pointer to 
move in one direction or the other against the pull of the 
magnets. The greater the current strength in the coils, the 
more will the needle be deflected. The current strength in the 
coils is dependent upon the voltage between A and B and by 
proper calibration, therefore, the instrument may serve as a 




voltmeter. In order to measure the deflection of the pointer 
a circular scale cut from a piece of stiff Bristol board is 
mounted at S, by being glued firmly to the top of the magnet, 
the pointer being so adjusted that it is about 1-16 inch above 
the scale. In our next chapter an explanation of the method 
of calibration will be given. 



EASY ELECTRICAL EXPERIMENTS. 



203 



CHAPTER LXIII. 



A PORTABLE VOLTMETER. 



PART THREE. 



It will be necessary to make some sort of a case to cover 
the working parts of our voltmeter in order to protect them 
from mechanical injury and to shield the pointer from cur- 
rents of air. A very nice case may be made from a piece of 
smooth sheet copper cut in the proper shape and soldered 

wherever necessary. The gen- 
eral shape of the case is shown 
in Fig. 5, which also gives an 
idea of the appearance of the 
finished instrument. 

The instrument as described 
may be used as a voltmeter or 
as an ammeter according to the 
method of connection. In either 
case, for the purpose of calibra- 
tion, a standard instrument is 
almost necessary— that is to say, 
some instrument whose read- 
ings are known to be approxi- 
mately correct. Let us suppose that our instrument is to be 
used as a voltmeter. The method of connection is shown in 
Fig. 6. Here A is the instrument described and B is the 
standard instrument, connected in parallel with A. A bat- 
tery shown at C must be provided sufficiently powerful to 
deflect the needle to its fullest extent. An adjustable resist- 
ance shown at P will also be required. Insert in series with 
A, a coil of wire represented merely at R. This is to be 
made of the same sized wire as is wound upon the coils of 
the voltmeter, and is a loose coil of wire. The process of 
adjustment is as follows: Suppose it is desired that A 
should give a full scale deflection on 30 volts. Make connec- 
tions as shown and adjust P until the standard reads at 30. 
Then insert enough resistance at R so that A will give the 




204 



EASY ELECTRICAL EXPERIMENTS. 



proper deflection. Probably this will cause a slight change 

in the reading of the stand- 

<Std^> ard so that p must De again 

\ A / \ / B adjusted. By alternately ad- 

justing P and R the proper 
deflection of A will finally be 
reached. After this R is to 
remain unchanged and lower 
points upon tto scale of A 
are obtained by adjusting P 
until the standard reads at 
the 4esir*HI! value when the 
itowrcro** of the needle of A 
can be marked with a pen. 
After calibration the resist- 
ance R may be fastened in- 
side the case of the volt- 
meter and connected in se- 
ries with the coils. It is 
then out of the way. 

Suppose, however, that the 
instrument is to be used as 
an ammeter. Then it will be 
necessary to connect across 
its terminals a low resistance as shown at S, Fig. 7. The 
instrument D is connected in series with a standard ammeter 
F, an adjustable resistance H, and a storage battery C. H 
is adjusted until the standard reads at the desired value 
when S is adjusted until D gives the proper deflection. This 
will cause a change in the reading of the standard, neces- 
sitating a readjustment of H and another adjustment of S. 
Having once fixed S, however, it is not to be changed. It 
can be soldered permanently to the terminals of the instru- 
ment and coiled up inside the *&&q. Th^ various points upon 
the scale of D may be obtalnea r»y adjusting H until the 
standard reads the proper value when the position of the 
pointer D is marked with a pen as before. 

The instrument may, therefore, be set up either as an am- 
meter or a voltmeter and ought to be of considerable value 
to the amateur. 




EASY ELECTRICAL EXPERIMENTS 



205 



CHAPTER LXIV. 



A PORTABLE BATTERY AND SWITCHLESS LAMP. 



rfz%> 



A very convenient and durable portable battery and lamp can 
be constructed as follows: 

The details of construction are shown in Figures 1 and 2. The 
lamp requires no switch, this result being obtained by means of 
a specially designed battery jar. 

The design of this jar is such that the electrolyte can act upon 
the plates of the battery only when the container is placed in a 
certain position, and this 
position also places the 
lamp at the proper angle 
for the diffusion of light to 
the best advantage. The 
outer casing is wood. 

The dimensions of these 
pieces may be 9 in. x 9 in. x 
% in. Each piece should be 
thoroughly sandpapered, , 
and the joints, which are to 
be mitred, should be put to- 
gether with glue and se- 
cured by flat head wood 
screws. Four screws should 
be used at each joint. 

The inside container, or 
battery jar proper, consists 
of eight pieces of white 
wood indicated by the nar- 
row edges of darker shade and designated by the letters C, D, E, 
F, G and H. 

The dimensions of these pieces are as follows : C — 7 in. x 7 in. x 
y 2 in- ; D — 7 in. x 4 in. x y 2 in. ; E — 7 in. x 3% in x % in. ; F — 7 in. 
X 3 in. x % in. ; G — 7 in. x 7 in. x % in. ; H — 7 in. x 3% in. x % in. 

Before assembling the parts of the inside container a one-inch 
hole, I, should be bored in piece E for the purpose of filling the 
interior with electrolyte. When the device is in use, this hole is 
closed by the plug P. Three holes are also to be bored in piece D. 




Figure 1. 



206 EASY ELECTRICAL EXPERIMENTS 

Two of these holes are designed to receive the lugs of the bat- 
tery plates A and B as shown, and the distance between them is 
one inch, while the distance between hole B and piece H is one inch 
also. Two pieces of soft rubber tubing, or old rubber hose should 
be snugly inserted into these holes in order to properly insulate 
the electrodes passing through them. 

A third hole about one-half inch in diameter is also to be bored 
in piece D into which a glass tube T with ends bent as shown is 
to be inserted. This is done to permit the gas generated by the 
battery to escape through the tube when it is in use. The two sides 
of this L-shaped container are of the same size and should be cut 
to the shape of the jar when completely assembled. The corners 

should be careirully glued with a 
liquid glue and all parts should be 
secured in substantial position by 
%-inch flat-head iron screws. Hav- 
ing secured all parts in their proper 
places the next step to be taken in 
the construction of the container is 
to make the interior surface abso- 
lutely acid-proof. To prevent the 
acid from leaking out of the con- 
tainer, the cracks can be filled by ap- 
Figure 2. plying a thin coating of melted pitch 

or asphalt to the inside surface as 
shown by the heavy black line. The best method of accomplishing 
this is to melt a few pounds of asphalt in a kettle and then after 
pouring in a sufficient quantity through the rubber tube holes at A 
and B, plug all holes and tilt the container in such a manner as to 
cause the melted tar to run into all corners and cracks, after which 
it may be permitted to cool. This process should be repeated until 
the entire surface of the interior is thoroughly coated with the insu- 
lating and acid-proof material. In order that the battery plates and 
glass tube T may be put in their proper locations after the coating 
of asphalt has cooled it will be necessary to remove one of the 
sides of the container. Figure 2 shows the shape of the battery 
plates, one of which, M in Figure 1, is the carbon plate, and Z is the 
zinc plate. 

Each plate measures 6 in. x 3 in. x -^ in. and is fitted with a 
lug of the proper size to pass through the insulated holes at A and 
B. In each lug a hole is to be drilled as shown in Figure 2 for 
receiving an 8-32 binding post screw for connections. After the 
battery plates and tube T are in position, the side of the container 
may be replaced and permanently secured. 

In order to produce a complete joint when putting this side 




EASY ELECTRICAL EXPERIMENTS 207 

in place it should be coated with the melted asphalt while ex- 
posed, and again warmed when closed. 

The mixture composing the electrolyte for the battery is made 
up as follows: 

Potassium bi-chromate 1 

Concentrated sulphuric acid 3 

Distilled water 10 

By placing the cabinet on its side J, and removing plug P, a 
sufficient quantity of this solution may be poured through hole I 
to fill the bottom chamber up to the proper height to cover the 
plates when the cabinet stands in the position shown in Figure 1, 
which is the proper position for supplying current to the lamp at 
Xi, which is a two-volt incandescent lamp enclosed in a metallic 
reflector, the opening of which may be fitted with a condensing 
lens. 

The dimensions of this reflector is a matter of choice and the 
size of the opening to be cut in the outside casing depends upon 
the dimensions of the reflector. 

Connection is made with the central terminal of the lamp by 
means of a short copper strip N, secured as shown in Figure 1, 
wrhile the other connection is made from the reflector. Flexible 
conductors are used from these terminals to the battery terminals. 
Having made all connections, sufficient melted paraffine should be 
poured on top of part D to cover the binding posts. This when cool 
will form an insulating compound O, which will protect the parts. 
With the apparatus in the position shown in Figure 1, the electro- 
lyte solution S covers the battery plates to the proper height, and 
current is being supplied to lamp L. When the lamp is not needed, 
the generation of current may be instantly stopped by simply turn- 
ing the cabinet on its side J. This will cause the solution to occupy 
the other compartment of the container, thus leaving the battery 
plates bare; the result being that the lamp is extinguished, and 
all unnecessary eating away of the zinc plate by the acid solution 
is also prevented. 

When the lamp is again needed, all that is necessary is to re- 
place the cabinet in its former position, allowing the solution to 
•again cover the surface of the plates, when the generation of cur- 
rent will begin at once and the lamp will be lighted. No switch 
is required, hence the name "switchless" lamp. 

An extra handle can be attached to the side K of the cabinet to 
be used in carrying the device from place to place when current is 
not needed, side K at such times being the top and the extra handle 
will be found to be a great convenience. 



INDEX 



A 

Apparatus for Measurement of Resistance 77 

Arc Lamp 160 

Armature and Commutator 33 

Armature Core, how to make 46a 

Armature, how to wind 46d 

Assembly of Motor 43 

Automatic Circuit Closer 172 

B 

Battery, Laboratory Storage, How to Make One 89-92 

Battery, Simple Experimental 1 

Battery, an Experimental 163 

Battery, Storage, How to Make One 123 

Bell, Electric, How to Make One 95-9& 

Bomb, How to Make an Electric ; 166 

C 

Cell, Dry, How to Make One 6a 

Cells, Various Types of 9 

Circuit, an Automatic Closer 172 

Coil, Induction, How to Make One 21 

Commutator and Armature 33 

Condenser, Electric, How to Make One 87 

D 

Dry Cell, How to Make 60 

Dynamo, Small, The Design of 131-134-137-140-143 

E 

Electric Bell, How to Make 95-9$ 

Electric Condenser, How to Make 87 

Electric Locomotive, How to Make 191-194 

Electric Motor, Simple 24 

Electric Units 28 

Electrophorus, How to Make 84 

Electric Plating at home, How to Do 107-111-114 

Engine, How to Make an Electric 169> 

F 

Field Magnet, The , 36 

Field Magnet, Winding the 40 

Fire Alarm Telegraph 175-180 

G 

Galvanometer, for Measurement of Resistance 77 

Galvanometer, How to Make a Tangent One 13 

Galvanometer, Simple 5 

Gyroscope, How to Make One 147-150-15$ 



H 

How to do Electro Plating at Home 107-111-1141 

How to make a Dry Cell 6G 

How to make an Electric Bell • 95-98 

How to make an Electric Bomb 166 

How to make an Electric Condenser 87 

How to make an Electric Gyroscope 147-150-153 

How to make an Electrophorus 84 

How to make an Electric Engine 169 

How to make an Induction Coil 21 

How to make Laboratory Storage Battery 89-92-123 

How to make a Motor 1-20 H. P 33-36-40-43 

' How to make a Rheostat 101-104 

How to make a Set of Telegraph Instruments 47-51-54 

How to make a set of Telephone Instruments 63-67-71-74 

How to make a Simple Telephone 127 

How to make a Tangent Galvanometer 13 

How to Wire and Use Telegraph Instruments 57 

I 

Induction Coil, how to make 21-181-183-186-189 

Instruments, Telegraph, how to make a set of 47-51 

Instruments, Telephone, how to make a set of 54-63-67-71-74 

L 

Xamp, An Electrically Lighted 157 

Lamp, A Simple Arc 160 

Locomotive, how to make an Electric 191-194 

M 

Measurement of Resistance 77 

Magnet, The Field 36 

Magnet, Field winding it 40 

Magnetism 17 

Motor, Assembly of 43 

Motor, 1-20 H. P., how to make 33-36-40-43 

Motor, a Simple Electric 24 

R 

Resistance, the measurement of 77 

Rheostat, how to make one 101-104 

S 

Simple Electric Motor # 24 

Simple Experimental Battery mm [ m 1 

Simple Galvanometer . " " " 5 

Storage Battery, Laboratory, how to make one 89-92-123 

T 

Telegraph, a Model Fire Alarm 175-180 

Telegraph Instruments, how to make a set of ".".'.".'.47-51-54 

Telegraph Instruments, how to wire and use 57 

Telephone Instruments, how to make a set of ." .63-67-71-74 

.Telephone, Simple to make one 127 



iii 
U 

Units, Electric -.-. 2£ 

V 

Voltmeter, Simple adjustment of 120 

Voltmeter, Simple, Construction and use of 117 

Voltmeter, A Portable 197-200-203 

W 

Wire and Use Telegraph Instruments, How to do it 57 

It would be a great assistance to the students of Electricity if they would, 
purchase a copy of The Handy Electrical Dictionary. 

Vest pocket edition, compiled and edited by Wm. L. Weber, M. E. An 
entirely new edition, brought up to date. This is a work of the highest 
standard. In this work every used electrical word, term or phrase will be found 
intelligently defined. A practical handbook of reference, containing definitions 
of about 3,000 distinct words, terms and phrases. This work is absolutely 
indispensable to all who are interested in electrical science, from the higher 
electrical expert to the everyday electrical workman. In fact, it is a complete 
Electrical Encyclopedia, and should be in the possession of all who desire to keep 
abreast with the progress of this branch of science. 

Cloth, red edges, indexed, 25c; full leather, gold edge, indexed, 50c. 

Sent postpaid to any address upon receipt of price. 

Frederick J. Drake & Co., Publishers, 



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